Hey pascalec, this is a change we're hoping to land in Nightly to ride the Firefox 69 train. The idea here is that users who want to use userChrome.css or userContent.css files will have to flip the `toolkit.legacyUserProfileCustomizations.stylesheets` pref to true in order for them to take effect. This is to avoid checking the disk for those files unnecessarily, which adds main-thread IO, and can jank the browser. One thing to note is that Firefox 68 is going to go out with bug 1550157, which automatically sets that pref for users that have a pre-existing userChrome.css or userContent.css file, so we expect that to help avoid annoying most people who have those types of customizations already - they shouldn't notice a difference. From Firefox 69 and onward though, folks who want to use userChrome.css or userContent.css will also need to flip the toolkit.legacyUserProfileCustomizations.stylesheets pref. What's the best way to message this out to the right communities of users who will want to know this stuff?
Bug 1541233 Comment 35 Edit History
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Hey pascalc, this is a change we're hoping to land in Nightly to ride the Firefox 69 train. The idea here is that users who want to use userChrome.css or userContent.css files will have to flip the `toolkit.legacyUserProfileCustomizations.stylesheets` pref to true in order for them to take effect. This is to avoid checking the disk for those files unnecessarily, which adds main-thread IO, and can jank the browser. One thing to note is that Firefox 68 is going to go out with bug 1550157, which automatically sets that pref for users that have a pre-existing userChrome.css or userContent.css file, so we expect that to help avoid annoying most people who have those types of customizations already - they shouldn't notice a difference. From Firefox 69 and onward though, folks who want to use userChrome.css or userContent.css will also need to flip the toolkit.legacyUserProfileCustomizations.stylesheets pref. What's the best way to message this out to the right communities of users who will want to know this stuff?