1698132 - Improve caching behaviour of -moz-bool-pref

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, enhancement)

Description

[Mike Conley (:mconley) (:⚙️)]

In bug 1697315, I added some CSS rules that use moz-bool-pref for a preference browser.proton.enabled. I ended up tripping a test failure in browser_preferences_usage.js, because apparently I was accessing that preference too often during startup.

That's not exactly expected. From our experience using moz-bool-pref, the preference should be read once and cached somehow. Generally, preference flips have not affected moz-bool-pref until restart. It's not clear to me how that caching works, and why it's not working in this case - though perhaps it's related to the fact that the moz-bool-pref read was occurring within checkbox.css, which is a CSS stylesheet scoped to a custom element.

Comment 1

[Marco Bonardo [:mak]]

I just hit the same for browser.proton.urlbar in Bug 1698834. I'll have to add another exception until it merges with the main pref.

Comment 2

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1698132 - Convert proton pref checks from @supports rules to media features. r=mconley,Gijs

This means that dynamic changes will be handled correctly, we can use
StaticPrefs, etc.

Comment 3

[Emilio Cobos Álvarez [:emilio]]

So -moz-bool-pref as is is wontfix, I think, but we can do better for specific prefs, and after the patch above adding these is relatively straight-forward (basically, defining the relevant token / pref pair in StaticAtoms / StaticPrefList.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/b5e5ac2c512c
Convert proton pref checks from @supports rules to media features. r=Gijs

Comment 5

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/b5e5ac2c512c