Description of problem:
This issue happens only with Offscreen surfaces and OMTC enabled as described in https://lists.fedoraproject.org/pipermail/devel/2015-August/213645.html

With "in-browser notifications" I mean those things called GtkInfoBar in Gtk. They show up e.g. when firefox blocks a popup. They are used e.g. by the HTTPS finder addon to tell you that HTTPS was found, or by the requestpolicy addon to ask before forwarding if you disabled automatic redirection.

Version-Release number of selected component (if applicable):
firefox-40.0.3-1.fc22.x86_64, happened on 39.x releases too afaik.

How reproducible:
often

Steps to Reproduce:
1. use a website or addon that displays these notifications. In my case this is RequestPolicyContinued beta from [1] with "block all connections" set to true on about:requestpolicy?defaultpolicy
2. go to https://www.ssllabs.com/ssltest/
3. run the ssl test for any website not cached. Use a rarely known URL. After some time firefox should display a notification bar because RequestPolicyContinued blocked the redirection/page reload.

Actual results:
the website displayed in firefox flickers while fading in and out notification bars.

Expected results:
notification bar should fade in and out without flickering the screen. In fact I don't need the animation at all, but I can't turn it off.

Additional info:
Previously, with OMTC enabled but Offscreen surfaces disabled firefox used to crash in these cases. I reported these crashes to mozilla using the builtin firefox crash reporter. But I stopped doing so since I doubt anyone will look at this over at mozilla. Is there any reason why abrt/libreport is set to not report firefox crashes in /etc/abrt/abrt-action-save-package-data.conf ?

[1] https://requestpolicycontinued.github.io/