Redesign JS Hook injection
Georg Koppen found a race condition in our Javascript hook application that allows the hooks to be bypassed. Right now, they only exist to project window.screen and associated resolution information, so we can probably just replace them with a patch (#5856 (closed)).
However, the technique is useful, and we might want to use it in the future as opposed to Firefox patches to tweak other APIs (#5293 (moved), #5666 (moved))... This ticket is to see if we can create a more reliable way of injecting js hooks that is more directly supported by the browser.
Or, maybe we just want to patch Firefox for everything. The patch approach will help ensure stuff stays on Mozilla's radar.