User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:56.0) Gecko/20100101 Firefox/56.0 Build ID: 20170728100358 Steps to reproduce: Upgraded to the newest nightly version and attempted to open the applications (hamburger) menu, bookmarks menu, or any other toolbar menu with an animation. Disabled plugins, created a new profile, opened in safe-mode. Reproducible in each instance. Actual results: The menus did not open. Note that this issue only presents itself in a window manager like i3, Openbox, etc. The menus worked normally in Gnome and KDE. Expected results: The menus should open as normal.