COMMAND REFERENCE

fxcss try

bash

fxcss try adamXweb/WhiteSurFirefoxThemeMacOS
fxcss try github.com/owner/theme --with compact-tabs
fxcss try owner/theme --info            # report what's there, launch nothing

Test-drive a theme before committing to it. Downloads it, installs it into a throwaway profile, and opens Firefox so you can actually use it. Your own profile is never touched — close the window and nothing remains.

It reports what it found before doing anything:

example

  adamxweb/whitesurfirefoxthememacos  ★614  MIT
    MacOS Big Sur like theme for Firefox on MacOS & Windows.
    latest release   v1.6.3  (2025-07-26)
    latest commit    b10c574  (2025-07-26)  Merge pull request #167 …

  fetching release v1.6.3 …
  theme found at the repository root  (39 stylesheets, 134 KB)

  This theme ships install.sh. fxcss does not run it —
  it installs the files itself, which is all those scripts do.

  Options its README documents:
    -c     Left hand side tab close button
    -p     Makes tabs height compact like current Safari
    …

  Optional stylesheets you can layer on with --with:
    compact-tabs, hideextension, noidentity, tabs-swapclose, …

Releases are preferred over branch tips, since that is what the author blessed; --commit takes the latest commit instead, and --ref takes any tag, branch or SHA. --with name,name layers on the theme's optional stylesheets so you can see a variant without hunting through install flags. --shot dir captures the standard screenshots instead of opening a window, and --keep dir leaves the download behind so you can start editing it with watch.

It does not run the theme's install script

fxcss installs the theme's files and supported preferences itself. It reports any installer it finds and reads the options documented in the theme's README. A theme that requires additional setup outside those files and preferences may still need manual steps.

What is left is the theme's own content: CSS, SVG, and occasionally a .js file. Firefox does not execute a .js file sitting in a profile's chrome folder; that requires an autoconfig hook in the application directory, which fxcss does not create. Archives are size-capped and path-checked on extraction, and symlinks in them are skipped.

If you decide you want the theme permanently, fxcss install is the same resolution and the same file copying — pointed, deliberately, at your real profile.

Getting started fxcss install