2023-2026
⬇️ Historical comparison 🔸 Useful addons + about:config 🔸 Other ⬇️
CSS Calendar - FF153 (beta - 1.Aug.2026 /// final??? - 15.Aug.2026) 🔸 TB - skip 1 ESR release + 1 month (2027)
android - 📥 desktop mode as default + fullscreen
Firefox CSS - 📥 153⠀📥 themes (light)⠀📥 Autohotkey v1.1 ⬇️
ESC (hold/double) - Page with/out style
Tab (hold, double) - switching between last 3 tabs
F2 - Find Previous (searchbar)
INS - Focus Address bar (press) / Address bar history (hold) / ESC (double)
Del (hold) - copy URL. Activate bottom Notepad++, keywait CTRL+V and activate bottom Firefox is disabled
Home - New Tab (press) / Address bar bookmarks (hold) / ESC (double)
END - Close Tab
PgUp - Go one Tab to Right (press) / Address bar tabs (hold) / ESC (double)
PgDn - Go one Tab to Left
F1 - Bookmarks (press) / History (hold) / Downloaded (double) [places.xhtml, open in tab 1, focus on search] + "Enter" for opening in new tab (press/hold), CZ/EN FF
YoutubeFullscreenDumbAdSkipper (numenter - Mute+show player ui /// numdot - unMute+skip ad /// 2560/1920x1080)
Default hotkeys
F3 - Find Next (searchbar)
MButton (close tab / open bookmark(s))
Alt+F4 (close FF)
Win+arrows (minimize/maximize/restore window)
CTRL+TAB (ALT+TAB for FF)
CTRL+UP/DOWN (page up/down)
Tab, Shift+Tab (UI elements switch)
Thunderbird CSS - 📥 140⠀📥 115⠀📥 theme⠀📥 Autohotkey v1.1 ⬇️
F2 - Find Previous (searchbar, press) + Rename (hold)
F3 - Find Next (searchbar) - works without script
INS - Focus search bar (press) / Focus filter bar (hold)
END - Close Tab
PgUp - Go one Tab to Right
PgDn - Go one Tab to Left
RCtrl - Paste message to archive (press+hold) - context menu
prefs.js file) copy into your ThunderFox profile (about:profiles). If you don't want to modify web content (especially first global row may cause issues on some websites - Google login doesn't work without playing animation on first attempt - F5, Steam images do not repeat endlessly when hovering over them with mouse, ...), just delete userContent.css file. If you want to return removed buttons/icons and some other small things, just delete upper "Delete me" part in userChrome.css file and all except first 5 lines in user.js file (CSS 132 / ESR+)
■ Firefox/Thunderbird installers can be extracted by WinRar/7-Zip and then used without installation. Profiles can be manually created and run via thunderfox.exe -p or automatically created (if it doesn't already exist. Auto may not work in very old FF) and run via (example) thunderfox.exe -profile "a:\000". Offline mode thunderfox.exe -offline
■ Most of colors I've changed are pink (FF00A3, E20074, pink), orange (FB7914) and in url (fdd7aa, springgreen) - they can be easily found/replaced. CSS files can be edited and tested even by your pet = data loaded from it are only temporary in RAM memory and after deleting files there is no trace of them in profile or Firefox itself.
■ Feel free to report CSS issues (from 115+) either as an "Issue" or via email = it seems that number of features/GUI elements in FF/TB is growing, and it’s possible that I’m not even aware of some of them + I’m using old Win7 2009. If some GUIs haven’t been edited by me for compactness, it means they’re unimportant to me, and I might also create bugs by doing so. FFCSS Gen1 (2-132) is very buggy. Of course, all bugs can be “fixed” by removing certain parts of CSS code.
🚫disabling downloading updates - updates in C:\ProgramData\Mozilla or C:\Users\XXX\AppData\Local\Mozilla (restrict access). However, these method can cause a bug in Thunderbird (inability to open settings and browse emails)
🚫disabling compatibility check of profile - compatibility.ini (restrict access). Profile may or may not be damaged, but its use will no longer be decided by someone else
■ CSS FF59- opening menu bar through ALT+arrows (2-LINE)
■ FF117+ is working again in Win7 (in my case without audio/video = system without codecs = unlike older FF, those for Win10+ are probably dependent on system, or kernel issue) kernel1 2 3 or FF [without user_pref("media.rdd-wav.enabled", false); (user.js) FF140/153 may not run in Win7]
■ CSS TB115+ has a limited length of splitter (for window resizing) to avoid interfering with some icons
■ userContent.css (for testing) - better font + static web * {font-family: sans-serif !important; animation-duration: none !important; animation: none !important; transform: none !important; rotate: none !important;}
■ CSS created in Win11 2021 (virtual machine) - FF119/132
■ Versions I used -
FF Win 2006+ 1-64 43 52 64 68 73 78 84 89 CSS 99 115 140 153 (internet explorer offline 2004-2006)
TB Win 2016+ 38 45-68 78 91 99 109 115 CSS 140
FF android 2024+ 132 (chrome 71 2021-2024)
■ FF49 (2016) general.useragent.override -
youtube, google drive (2026) Mozilla/5.0 (PlayStation 5 3.03/SmartTV) AppleWebKit/605.1.15 (KHTML, like Gecko)
■ To view images in full size (42, 1920x1080, earlier 2560x1080) you can save page as Web page, complete (7MB)
153 (2026-2027) - 2-LINE -
153 (2026-2027) - DEFAULT -
140 (2025-2026) - 150% DPI + narrow scrollbar + "mail.uidensity", 0 (Compact 👍).
140 (2025-2026) - 150% DPI + narrow scrollbar + "mail.uidensity", 0 (compact 🤔).
140 (2025-2026) - 3-LINE -
140 (2025-2026) - DEFAULT -
140 (2025-2026) - context menu+folder+download - 150% DPI
119 (2023) - DEFAULT -
119 (2023) - 3-LINE -
140 - Gen2 (2025-07) - 2-LINE -
140 (2025-2026) - DEFAULT -
132 (2024) - 2-LINE -
132 (2024) - DEFAULT -
119 (2023) - 2-LINE -
119 (2023) - DEFAULT -
109 - (2023) - 2-LINE -
109 (2023) - DEFAULT -
99 Gen1 (2023-03) - 2-LINE
99 (2022) - DEFAULT
89 (2021) - 2-LINE
89 (2021) - DEFAULT
79 (2020) - 2-LINE
79 (2020) - DEFAULT
69 (2019) - 2-LINE
69 (2019) - DEFAULT
59 (2018) - 2-LINE
59 (2018) - DEFAULT
49 (2016) - 2-LINE
49 (2016) - DEFAULT
39 (2015) - 2-LINE
39 (2015) - DEFAULT
29 (2014) - 2-LINE
29 (2014) - DEFAULT
19 (2013) - 2-LINE
19 (2013) - DEFAULT
9 (2011) - 2-LINE
9 (2011) - DEFAULT
3.5 (2009-2011) - 2-LINE
3.5 (2009-2011) - DEFAULT
2 (2006-2008) - 2-LINE
2 (2006-2008) - DEFAULT
115 (2023-2024) - 150% DPI + narrow scrollbar + "mail.uidensity", 0 (Compact 👍). 1920x1080
115 (2023-2024) - 150% DPI + narrow scrollbar + "mail.uidensity", 0 (compact 🤔). 1920x1080
Enhancer for YouTube
YouTube Ad Auto-skipper
Hide YouTube Fullscreen Controls
YouTube Scrollable Fullscreen
YourCodecs - blocking AVC can fix broken youtube (An error occurred. Please try again LATER) - Windows without audio/video codecs
SaveFrom.net helper
Image Video Block
Disable HTML5 Autoplay - issues with cloudflare (seznam.cz+cncenter.cz+pcgw) = maybe not (2026-07)
Large Image Blocker - can save up to 100+MB per Steam page by blocking GIF videos+other unoptimized images
I still don't care about cookies
Print Edit WE
Save Page WE
User-Agent Switcher
Hide My IP Free
QRCode Scanner
Load Background Tabs Lazily - resource limiter (without it, some pages may require a refresh if they don't load within time limit) + ban limiter (DDoS attack)
android new tabs in foreground
uBlock Origin - ("My Filters")
■ disable canvas (animation,...) = ##canvas
■ how disable multimedia (streaming=downloading)?
dpi
layout.css.devPixelsPerPx
turning off full screen warning
full-screen-api.warning.timeout;0
default zooming of PDF files
pdfjs.defaultZoomValue;page-width
find in page - colors
ui.textSelectBackgroundAttention
ui.textHighlightBackground
ui.textHighlightForeground
new tab - color
browser.display.background_color;#eeeeee
scrollbars
widget.non-native-theme.scrollbar.size
widget.non-native-theme.win.scrollbar.use-system-size
widget.non-native-theme.scrollbar.size.override
widget.disable-dark-scrollbar
widget.non-native-theme.win11.scrollbar.force-overlay-style
widget.windows.overlay-scrollbars.enabled
disabling tooltips when hovering over bookmarks
browser.chrome.toolbar_tips
disable animations (interface of program and website itself) - probably no need to be afraid of blindly toggling "animat" and "transition" preferences
browser.fullscreen.animate;false
browser.tabs.animate;false
image.animation_mode;none
ui.prefersReducedMotion;1
svg.disabled;true
full-screen-api.transition-duration.leave
full-screen-api.transition-duration.enter
set compact density immediately by number 1
browser.uidensity
disable graphical user interface "Proton"
browser.proton.enabled
disable graphical user interface "Nova"
browser.nova.enabled
address bar - number of items
browser.urlbar.maxRichResults
address bar - disable autoFill
browser.urlbar.autoFill;false
address bar - disable search engine
keyword.enabled;false
address bar - disable "Firefox suggest"
browser.urlbar.groupLabels.enabled;false
address bar - disable faded font
browser.urlbar.formatting.enabled;false
address bar - hide reader icon
reader.parse-on-load.enabled;false
tabs - disable previews when dragging
nglayout.enable_drag_images;false
tabs - minimum width
browser.tabs.tabMinWidth
tabs pinned - disable autoreload
browser.sessionstore.restore_pinned_tabs_on_demand
disable request to delete settings when browser is not started for a long time
browser.disableResetPrompt;true
disable query to enable DRM
browser.eme.ui.enabled;false
slow Firefox startup - turn off notifications
browser.slowStartup.notificationDisabled
do not turn off firefox when closing last tab
browser.tabs.closeWindowWithLastTab;false
open in tabs only
browser.link.open_newwindow.restriction;0
location query
geo.enabled
disable "insecure login" warning
security.insecure_field_warning.contextual.enabled;false
ctrl+shift+j
devtools.chrome.enabled;true
disable autoplay
media.autoplay.enabled;false
media.autoplay.allow-muted;false
media.autoplay.default;5
disable enforcement of signing add-ons
xpinstall.signatures.required;false
security.signed_app_signatures.policy
disable blacklisting of add-ons
extensions.blocklist.enabled;false
not to allow arbitrary banning of add-ons
extensions.legacy.enabled;true
do not save list of currently opened tabs to disk = reduce writing to SSD
browser.sessionstore.resume_from_crash;false
save interval = reduce writing to SSD
browser.sessionstore.interval
do not create bookmarks backups
browser.bookmarks.max_backups;0
disabling automatic page refresh
accessibility.blockautorefresh;true
maximum cache size on SSD (increase 1GB limit)
browser.cache.disk.capacity
browser.cache.disk.smart_size.enabled;false
maximum size of cached file on SSD
browser.cache.disk.max_entry_size
cache isolation
browser.cache.cache_isolation;true
connection timeout
network.http.connection-timeout
firefox.exe - priority "normal"
dom.ipc.processPriorityManager.enabled;false
limiting number of firefox.exe processes
fission
dom.ipc.processCount
suspend+throttling (background) tabs (+download function)
thrott
suspend
connections
dom.timeout.background_throttling_max_budget
another "limiter"
network.predictor.enabled
network.prefetch-next
FPS limiter
layout.frame_rate
gfx.display.max-frame-rate
reduce "Page Referrer" (from which webpage link was opened)
network.http.referer.disallowCrossSiteRelaxingDefault, true
disable "Page Referrer". May broke some websites (steamdb.info)
network.http.sendRefererHeader, 0
pretending different FF version or OS - example
general.useragent.override, Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:126.0) Gecko/20100101 Firefox/126.0/Yirxwl2yEK2v8lv4
show hidden addons in about:debugging
devtools.aboutdebugging.showHiddenAddons
disable PDF
pdfjs.disabled
acceleration, media support
layers.acceleration
webgl
canvas
media.hardware-video-decoding.enabled
media.hardware-video-decoding.force-enabled
media*enable
media*disable
audio*enable
264
gmp
dxva
media.hardware-video
media.wmf.dxva.d3d9.amd-pre-uvd4.disabled
media.windows-media-foundation.enabled
media.webaudio.enabled
media.play-stand-alone
ffvpx
opus
flac
ogg
wav
wmf
mp4 - can fix broken youtube (An error occurred. Please try again LATER), Windows without audio/video codecs, without mp4 support can be increased bitrate
webm
vp9
av1
mkv
disable endless downloading of tmpaddon* (~14MB per session) to TEMP folder
media.gmp-provider.enabled
media.gmp-widedevine.enabled
media.gmp-widevinecdm.enabled
media.gmp.decoder.enabled
image blocker
permissions.default.image;2
disable thumbnails/screenshots
browser.pagethumbnails.capturing_disabled
pageThumbs.enabled
screenshots.browser.component.enabled
can fix broken youtube
network.http.http3.enable;false
can fix non-functional addons
extensions.manifestV3.enabled; false
tooltip delay
ui.tooltipDelay, 50
if access to a particular page is forbidden for "security" reasons
security.tls.version.min
disable ads in about:addons
extensions.htmlaboutaddons.recommendations.enabled
extensions.getAddons.showPane
enable browser toolbox
user_pref("devtools.chrome.enabled", true);
user_pref("devtools.debugger.remote-enabled", true);
user_pref("devtools.debugger.prompt-connection", false);
disable tab grouping
browser.tabs.groups.enabled
disable picture in picture
picture-in-picture
disable translation query
browser.translations.enable
disable about:config warning
user_pref("browser.aboutConfig.showWarning", false);
user_pref("general.warnOnAboutConfig", false);
enable specific theme
user_pref("extensions.activeThemeID", "[email protected]");
user_pref("devtools.theme", "light");
disable def browser check
user_pref("browser.shell.checkDefaultBrowser", false);
disable close tabs warning
user_pref("browser.tabs.warnOnClose", false);
switch to opened tab
browser.tabs.loadInBackground
zoom 30-%
zoom.minPercent
toolkit.zoomManager.zoomValues
ai (blocked)
browser.ai
--------------------------------------------------------------------------------------------Thunderbird
disable blocked image notification
mailnews.message_display.disable_remote_image
https://github.com/topics/firefox?l=css&o=desc&s=stars
https://github.com/search?q=firefox+language%3ACSS&type=repositories&l=CSS&s=stars&o=desc
https://github.com/topics/thunderbird?l=css&o=desc&s=stars
https://github.com/search?q=thunderbird+language%3ACSS&type=repositories&l=CSS&s=stars&o=desc
https://firefoxcss-store.github.io/
https://www.reddit.com/r/FirefoxCSS/
https://www.userchrome.org/
about:about
chrome://browser/content/places/places.xhtml
https://firefox-source-docs.mozilla.org/devtools-user/browser_toolbox/index.html
https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly
https://support.mozilla.org/en-US/kb/keyboard-shortcuts-thunderbird
https://www.mozilla.org/en-US/firefox/releases/
https://www.thunderbird.net/en-US/thunderbird/releases/
https://whattrainisitnow.com/calendar/
https://connect.mozilla.org/t5/ideas/idb-p/ideas/tab/most-kudoed
Language packs (addons) are in xpi folder
https://ftp.mozilla.org/pub/firefox/releases/
https://ftp.mozilla.org/pub/fenix/releases/
https://ftp.mozilla.org/pub/thunderbird/releases/
https://mozilla.github.io/policy-templates/
https://caniuse.com/
https://www.deviceinfo.me/
https://explore.whatismybrowser.com/useragents/explore/software_name/firefox/
https://html5test.co/
https://test-ipv6.com
https://www.cloudflare.com/ssl/encrypted-sni
https://www.google.com/intl/en/ipv6/statistics.html
https://browserleaks.com/
https://georgebastock.github.io/CSS-Animation-Test/ - animation test
https://www.kevs3d.co.uk/dev/plasma - canvas animation test
https://codepen.io/keel/pen/xPzRyb - transform animation test
https://www.w3schools.com/css/css3_transitions.asp - transition animation test
https://www.w3schools.com/css/css3_shadows.asp
https://gsap.com/js/speed.html
https://haveibeenpwned.com
89 - Gen0 (2021-12) 150% DPI
99 - Gen0+ (2023-01) 150% DPI
--------------------------------------------------------------------------------------------suggestions for improvements
■ remove titles/checkboxes in "find in page" bar and replace them with buttons/icons (for addressbar+findbar overlay)
■ renaming bookmarks directly (long/short right mouse click)
■ tabs with play/pause button and hotkey (replace useless volume button)
■ combine "Edit Folder/Bookmark" in context menu into a single entry at one specific position (properties in ~FF79-)
■ popup status bar around mouse cursor
■ add-ons in "Customize Toolbar" menu
■ decrease mouse vert sensitivity when cursor approaches left/right sides of bookmarks (folders)
■ custom colours of folders for quick orientation (bookmarks)
■ javaScript CPU/GPU resource limiter (rotating ad can use entire CPU core regardless of its frequency), pause javaScript/animation ~5s after page is loaded (without reloading)
■ remove items from address bar (long/short right mouse click)
■ in places.xhtml show paths to items (searching)
■ better use downloads area (places.xhtml)
■ show download % + time in places.xhtml tab name
⭐153 - option switch tabs with hotkeys from places.xhtml (like ~FF89-)
■ custom tabs color (by domain), automatic grouping
■ move current tab at e.g. position 2 (CTRL+2)
■ tab switching by domain (custom hotkeys)
■ option to open a new panel in a new exclusive EXE process (prevent possible freezing/crashing of tabs in a shared process)
■ if all tabs in background are suspended, then have option to manually select tabs that will never be suspended
■ hide https://www. in address bar
■ separate audio/video cache from normal cache. What's the point of current setup where important cache data is overwritten by useless video that also reduces SSD lifetime? Constantly modifying NTFS permissions for cache folder (or using second FF profile with media support enabled) is not very comfortable...
■ sorting/selecting/removing in about:config, hide changed prefs
■ drag tabs without animation (~FF9- style)
■ hor tab bar scrolling with animation (~FF99- style, "ui.prefersReducedMotion"), custom roll steps, custom animation speed
■ UI autohide (as Win taskbar)
■ it is not possible to redirect "safebrowsing" folder from the ramdisk to SSD (NTFS links), which leads to constant downloading of the same data every time the profile is deleted and copied again (ramdisk)
■ if file "c:\Users\XXX\AppData\Local\Mozilla" exists, it is not possible to start FF (~v19+)
■ if file "datareporting" exists (in profile), FF freezes on start (~v119-132)
■ hide "new tab" labels (empty space is more visible)
■ bandwith limiter (browsing,download,upload)
■ reset addon settings
■ stream (download) audio only option, auto stop streaming video if FF/tab is in background (keep audio)
■ addressbar - "-" character as search exclude (like Google search and others)
■ custom cache write delays (reduce writes to SSD)
■ browser toolbox - reset changes button, pin styles button
■ "Copy URL" in context menus (bookmarks + tabs)
■ latest closed tabs list (long click to "List All Tabs" button)
■ drag&drop between multiple FF?
■ auto accept all Untrusted Certificates?
■ regular expressions (searching)
■ open vertical list of tabs by RButton+Wheel (release buttons = open selected tab) = like Notepad++
■ global selection of audio/video codecs and resolutions based on user's priorities/order (= not based on priorities/order of services themselves)
■ ability to move tabsbar with mouse wheel while a panel is holded (Lbutton+Wheel)
■ ability to copy text of tabs with a single click when using “Forward” “Back” buttons
■ to improve readability, increase highlighting of selected text (+1px above/below font)
■ right-click to close (popup) menus
Thunderbird
■ long click functions - e.g. for saving attachment(s)
■ hide some attachment sizes (b/kb)
■ keep user's icon color when selected
■ better use of the "Message Header Pane" space - partially solved ("from"). This addon does it quite well
■ disable+hide some days in calendar
■ remove "tree view" (done, CSS), colored first character instead? + global option of collapsing/expanding threads + remove arrows?
■ scrollable top bar (like tabs), use empty side/status bar space
android - backup restore profile. holding (some UI) automatically performs assigned action (close tab, open bookmarks, open link in new tab and switch to it, ...), disable double tap to select text, buttons on one side for one (left) hand (landscape mode), remove notification when opening/closing tab + other minor UI adjustments - e.g.
🤦android (5.5" 960x480, fullscreen) vs CSS - really only a 2,7 tabs can fit on the screen?🤦
Chyby webu -
mbank.cz - CTRL+C/V je zakázáno (pro umělé navýšení chybovosti+prodloužení procesu je nutné ručně přepisovat částky a pro potvrzení platby i náhodné texty) - přepnout stránku na "bez stylu" a zkopírovat text a ten vložit AHK skriptem (CTRL+SHIFT+V) ^+v::SendRaw %clipboard%
komunitni-preklady.org/ostatni-cestiny - stránka nejde uložit, vykresluje se pouze viditelná část - přepnout stránku na "bez stylu" /// nebo snížit DPI hluboko pod 1 + 1% velikost stránky + přepnout rozlišení obrazovky na výšku /// nebo použít Save Page WE a nastavit automatické zmenšení stránky před uložením
web.archive.org - stránka nejde zachytit (PCGW,sbazar) - na konec url přidat ?noredirect=1 (po pár hodinách po zachycení ale stejně může dojít ke smazání záznamu)
fanatical.com - nejde (klikat) vložit zboží do košíku a procházet historii objednávek atd. = nastavit PS5 User-Agent (addon "User-Agent Switcher"). (S největší pravděpodobností může být problém v nějaké změněné předvolbě v about:config)
myabandonware.com - nejde klikat na odkazy = přidat vyjímku "I still don't care about cookies"
mapy.com - problémy s nevykreslováním - šedé obdélníky = zkontrolovat oprávnění cache složky
datoid.cz - blokace (cenzura) některých stránek u operátora O2 se dá obejít zvýšením "Zapnout DNS over HTTPS pomocí:"
war-forum.net (hlavní stránka) - nekonečné stahování XML souboru (chat)
nekonečný download plnou rychlostí - zřejmě pokud jsou v FF zakázány audio/video kodeky (nebo pokud chybí ty výchozí ve Win?), tak na některých serverech
kurzy.cz - pscontent.playstream.media/manualUpload/f557xr5ocim66afifc/flickstree_video.mp4
w3schools.com - cdn.viously.com/video/3TXPgqkObK6/1-w240.webp
může dojít k brutálnímu bugu, kdy se místo přehrávání videoreklamy budou donekonečna (pokud uživatel nedostane ban na přehrávání reklam) stahovat/zahazovat části video souboru. Za 1 den je možné propálit stovky GB (1200GB SIM karta za 3000,- může být teoreticky jednou reklamou do 2 dnů vyčerpána). Jediné mě známé řešení je použít addon typu "Image Video Block" + "Disable HTML5 Autoplay" kteří jakékoli stahování utnou
aukro.cz (opotřebení SSD) - může docházet k podivným zápisům do "storage\default\https+++aukro.cz\cache\morgue" = 1 otočení kolečkem myši + pauza + opakovat = ~110MB zápis + ~110MB zápis + ...
Cloudflare auto browser check (bez obrázků) - stránky chráněné tímto systémem může být nemožné otevřít ve 2G sítích (~0,02-0,15 Mbit/s, nejen streamování 144p youtube videí není problém, ale na zkontrolování prohlížeče to prostě nestačí)
Website issues -
mbank.cz - CTRL+C/V is disabled (to artificially increase error rate and prolong process, it is necessary to manually rewrite amounts and random texts to confirm payment) - switch page to "no style" and copy text and paste it with AHK script (CTRL+SHIFT+V) ^+v::SendRaw %clipboard%
komunitni-preklady.org/ostatni-cestiny - page cannot be saved, only visible part is rendered - switch page to "no style" /// or reduce DPI below 1 + 1% of page size + switch screen resolution to portrait /// or use Save Page WE and set automatic page reduction before saving
web.archive.org - page cannot be captured (PCGW,sbazar) - add ?noredirect=1 to end of URL (however, record may still be deleted a few hours after capture)
fanatical.com - unable to add items to cart, view order history, etc. = set PS5 User-Agent (addon "User-Agent Switcher"). (Most likely, issue may be related to a modified preference in about:config)
myabandonware.com - links cannot be clicked = add exception "I still don't care about cookies"
mapy.com - problems with rendering - gray rectangles = check cache folder permission
datoid.cz - blocking (censorship) of certain websites by operator O2 can be circumvented by increasing "Enable DNS over HTTPS using:"
war-forum.net (homepage) - endless downloading of XML file (chat)
endless download at full speed - apparently, if audio/video codecs are disabled in FF (or if default ones in Win are missing?), then on some servers
kurzy.cz - pscontent.playstream.media/manualUpload/f557xr5ocim66afifc/flickstree_video.mp4
w3schools.com - cdn.viously.com/video/3TXPgqkObK6/1-w240.webp
may be a brutal bug where instead of playing video ads, video parts of file will be downloaded/discarded endlessly (unless user is banned from playing ads). Hundreds of GB can be used up in a single day (a 1200GB SIM card costing 120 EUR can theoretically be used up by a single ad within two days). Only solution I know of is to use an add-on such as "Image Video Block" + "Disable HTML5 Autoplay" which will stop any downloading
aukro.cz (SSD wear) - strange writes to "storage\default\https+++aukro.cz\cache\morgue" may occur = 1 mouse wheel + pause + repeat = ~110MB write + ~110MB write + ...
Cloudflare auto browser check (without images) - it may be impossible to open pages protected by this system on 2G networks (~0,02–0,15 Mbit/s, streaming 144p youtube videos isn't a problem, but this speed simply isn't enough to perform a browser check)