tbh I'm not even using this theme anymore, so not really up to date if it is broken in any new version of firefox or the like, am using (and ro recomend) the ShyFox theme right now, and am also looking into the Zen browser. I'd still like to keep this still working and maybe adding minor things, but not too commited to it (also with my limited time from life and other projects)

arcticfox theme

a theme for Firefox (and Sidebery, because it fancy) to make it look and somewhat behave like Arc browser on mac (rev 1)

a post with a video of it (lsightly earlier in dev) in use
little demonstration video with slightly newer version

🎊 features

• it kinda looks like Arc... that's the whole point
• kinda minimalistic
• has space to grab the window! (quite uncomon with themes that mess with the header bar)
• somewhat tested
• some strightforward(-ish) customization in the file

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ℹ️ addons to use

• sidebery for sidebar tabs, workspaces, groups...
• Firefox Multi-Account Containers for multiple logins
• Userchrome Toggle for toggling keeping the sidebar open (migh try creating an extensions for extra controls later, idk)
• (preference) themes from Firefox Color
  • another recomendation is Adaptive Tab Bar Color

how to install

yes, it is a bit contrived, but requires quite a specific setup to work well

• clone or download this repo locally
• install the listed addons
  • allow them to run in private windows
• open sidebery settings, go to 'help' and 'import addon data', then select the json file in sidebery/sidebery-data.json
• (if not showing already) open the browser sidebar and select the 'sidebery' sidebar
• in the settings for the 'userchrome toggle' extension, for the 'style toggle 1' put || in prefix (should also have the ending space) and apply changes (you migh also change the name to 'sidebar' if you want, and disable the 'display notification')
• select a firefox theme other than the 'system/auto' one (alpenglow also looks weird with it)
• disable the bookmarks toolbar
• disable the 'firefox view' button (that one at the top, left of the tabs, that firefox enables by default)
• reorder the browser toolbar widgets, they should be in the order
  • url-bar 'show sidebars'-button back forward reload spacer extensions-button overflow-menu hamburger-menu
  • the url bar must be the first item in the toolbar
  • there must be the sidebar button (for enabling the sidebar in private windows)
  • do this before applying the theme, it messes up the customize page
  • also set the density to 'normal' (it probably already is)

if you don't have userChrome (and browser dev tool) enabled (if you do, skip to the next part)

• go to about:config in the url bar (and accept the message)

• in the search bar insert toolkit.legacyUserProfileCustomizations.stylesheets

• if besides it there is a 'false', double click it, it should turn into 'true'

• right click anywhere in the page and open 'inspect' from the menu, it should open the dev panel

• click the three dots at the top right corner of that panel and in settings

• right at the bottom/right in the 'advanced' enable 'enable browser chrome and add-on debugging toolboxes' and 'enable remote debugging'

• close and re-open firefox

read next section

(if you want to activate the browser dev tool to inspect the browser ui and live change the css, press 'ctrl + shift + alt + i', it behaves like the normal dev tool but for the browser)

if/when you have userChrome (and browser dev tools) enabled

• write about:profiles in the url bar
• on the profile that is listed as 'default profile: yes' click 'open directory' for the root directory, it should open your file manager in that folder
  • on flatpak programs, this might show the wrong addres (/home/$user/.mozilla/...), the right address is (/home/$user/.var/app/$app_id/.mozilla/...)
  • it also might be something other than .mozilla if you're using a fork (librewolf)
• create (if doesn't exist) a sub folder called 'chrome' (exact name, all minuscule)
• put the file chrome/userChrome.css in there (the file must be called 'userChrome.css')
• if you want to use some extra options, put the folder opt/ there as well

(ℹ️ you might want to edit some settings in the css file, feel free to open it in your text editor, if you're on Windows there are some options in the file you need to uncomment to make it work better, do a 'ctrl + f' for WINDOWS in the file)

• close and re-open firefox, it should have the theme applied

using

• put your mouse on the left edge of the window to open the sidebar containing the tabs, url bar, and browser toolbar
• to keep the side bar open, on the extensions list from the toolbar, click the userchrome togge one, it should now keep the sidebar open (might glitch a bit)
• for workflow stuff, see the sidebery documentation
• you can drag the window from the top space or on the header bar when expanded

extra customization information and tips

• Window buttons like macOS
  • uncomment @import url('opt/mac_buttons.css'); in the imports section

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⚠️ btw

this theme is:

• buggy in some places
• janky in private windows or windows with the sidebar hidden by default
• only comfirmed to work on firefox 120 on linux, and on Windows 10 (with tweaks)
  • tested on some forks, and ESR or anything based on it (waterfox, floorp) does not work
  • the firefox version must fully support the :has() selector and css nesting
• best used with sidebery but I guess can be used with Tree Style Tab, didn't test tho
• not guaranteed to be 100% working out of the box, you might need to tweak it some
• probably doesn't work on macOS

(for some more info and warnings see the comments in chrome/userChrome.css)