Ubuntu 17.10 (GNOME Shell 3.26.2) STR: 1. Mousedown on tab and hold position without releasing mouse button. 2. Press Alt+Tab, release Tab and keep holding Alt so menu stays open. 3. Drag mouse cursor away from tab. 4. Release all mouse buttons and keys. 5. Attempt to drag something. Dragging is not possible for the rest of the session requiring the browser to be restarted to restore dragging ability. Log error: > Gdk-CRITICAL **: Window 0x7f56c02bea80 has not been made visible in GdkSeatGrabPrepareFunc Regression window: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=19b4265d0d568d232fb3a34705f947b6db7496dc&tochange=bf2bc1aa78c0b72d9b6b13f7a8c6ae61c60a51dc This regression also coincided with losing the ability to Alt+Tab while dragging and dropping (Bug 1276449). Most likely regressed by Bug 1170342.

Martin, do you think you could take a look here? I'm not sure what the status of bug 1170342 and related gtk3/xinput2/wayland work is these days. Thanks!

Sure, I'll look at it.

Yes, I can reproduce that. Works fine with MOZ_USE_XINPUT2=1 env set which means it's caused by disabled XINPUT2 support. Generally a dupe of Bug 1276449.