firefox: update documentation

[BreakingBread0]

Quick update to the firefox documentation. Theming uses userChrome.css as far as I can see but the respective config entry in about:config was not enabled by default on my setup.

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• Commit messages adhere to Stylix commit conventions
• Theming changes adhere to the Stylix style guide
• Changes have been tested locally
• Changes have been tested in testbeds
• Each commit in this PR is suitable for backport to the current stable branch

[trueNAHO]

Theming uses userChrome.css as far as I can see but the respective config entry in about:config was not enabled by default on my setup.

We are intentionally following Home Manager's programs.${firefox}.profiles.${profile}.extensions.force behavior:

• #1156 (comment)
• #881

However, I agree that this is non-untuitive since most Stylix applications apply theming to the best of their ability.

Either we mention programs.${firefox}.profiles.${profile}.extensions.force in the documentation, or we explicitly interface this option to make its existence more obvious.

CC: @Flameopathic, @awwpotato, @brckd, @danth

[danth]

the respective config entry in about:config was not enabled by default on my setup

We do try to enable the setting automatically when it's needed:

stylix/modules/firefox/each-config.nix

Lines 59 to 62 in 0902280

	settings = {
	"toolkit.legacyUserProfileCustomizations.stylesheets" = true;
	"svg.context-properties.content.enabled" = true;
	};

Note that this is only when Firefox GNOME Theme is selected, as in other cases we don't use userChrome.css. I believe that by default the theming for Firefox actually comes from our GTK module.

[danth]

We are intentionally following Home Manager's programs.${firefox}.profiles.${profile}.extensions.force behavior

Home Manager should produce an error when force is required:

https://github.com/nix-community/home-manager/blob/c7f4214faca2f196c551b767c12a70bfa0614510/modules/programs/firefox/mkFirefoxModule.nix#L823-L830