The change made in bug 1650488 is not to build an async zoom container if we're in fullscreen mode. This has the effect of not applying any APZ resolution to the page contents. On desktop, this is fine, since you can't zoom while in fullscreen mode. However, on Android, allowing the user to zoom is not the only purpose of the APZ resolution -- it's also used to respect the initial scale computed for mobile viewport sizing purposes (commonly, on desktop sites, to zoom out such that the ICB size (which for desktop sites is usually wider than the screen) fits visually into the screen size. So, I don't think the fix in bug 1650488 is appropriate for mobile. We may just want to restrict it to desktop only.
Bug 1659761 Comment 16 Edit History
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The change made in bug 1650488 is not to build an async zoom container if we're in fullscreen mode. This has the effect of not applying any APZ resolution to the page contents. On desktop, this is fine, since you can't zoom while in fullscreen mode. However, on Android, allowing the user to zoom is not the only purpose of the APZ resolution -- it's also used to respect the initial scale computed for mobile viewport sizing purposes (commonly, on desktop sites, to zoom out such that the ICB size (which for desktop sites is usually wider than the screen) fits visually into the screen size). So, I don't think the fix in bug 1650488 is appropriate for mobile. We may just want to restrict it to desktop only.
The change made in bug 1650488 is not to build an async zoom container if we're in fullscreen mode. This has the effect of not applying any APZ resolution to the page contents. On desktop, this is fine, since you can't zoom while in fullscreen mode. However, on Android, allowing the user to zoom is not the only purpose of the APZ resolution -- it's also used to respect the initial scale computed for mobile viewport sizing purposes (commonly, on desktop sites, to zoom out such that the ICB size (which for desktop sites is usually wider than the screen) fits visually into the screen size). It appears that this remains important in fullscreen mode, too, i.e. the fullscreen page contents are still sized to the ICB size (and with a fixed width in the meta viewport tag, the ICB size does not change based on being on fullscreen mode). So, I don't think the fix in bug 1650488 is appropriate for mobile. We may just want to restrict it to desktop only.