Eden Chuang
c28bc7e5ca
animationsPlayBackRateMultiplier is a synced BrowsingContext field whose CanSet requires IsTop(). When a root target actor (e.g. the Browser Toolbox) has an iframe selected as the currently targeted document via the iframe picker, this.browsingContext is no longer the top context, so setting the multiplier on it crashed with "CanSet failed for field(s): AnimationsPlayBackRateMultiplier". Set the field on this.browsingContext.top instead, which matches the field's getter (which reads from Top()) and is a no-op for the regular tab toolbox where the targeted context is already top. Differential Revision: https://phabricator.services.mozilla.com/D305790