STR: - run Firefox with a new profile - install Ghostery, enable alert bubble (default) - open website that uses trackers, scroll Result: Firefox scrollbars disappear when the Ghostery alert bubble is shown. The scrollbar area is black at first and then turns all grey. I am not quite sure if this happens on every website. Regression: Last good revision: 152ef25e89ae (2014-09-10) First bad revision: 98ea98c8191a (2014-09-11) Pushlog: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=152ef25e89ae&tochange=98ea98c8191a No more inbounds to bisect Last good revision: 7a702947b274 First bad revision: 0bf2ecd85d9a Pushlog: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=7a702947b274&tochange=0bf2ecd85d9a

Christian, thank you for the bug report! Dupping forward to bug with clear regression changeset.