User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:44.0) Gecko/20100101 Firefox/44.0 Build ID: 20151013030225 Steps to reproduce: Try and move a tab in firefox nightly using gtk3. Actual results: For an instance a little square preview pops up near the cursor, but quickly disappears and even though I’m still holding the left-click button the cursor now moves without the tab, thus making it impossible to re-order the tabs with the mouse. The keyboard shortcuts aren’t working either, but I don’t know if they ever did. Expected results: The tabs should be movable.

The tabs can’t be moved in Firefox stable either. I’m now assuming this is a bug introduced when upgrading GNOME 3.18. I don’t know if this is a bug at their end, or if some gtk3 api has changed and Firefox needs to change to use it.

Turns out they can be movide in firefox stable, but I don’t think firefox stable is using gtk3 yet. It certainly isn’t using my dark gtk3 theme.

Does disabling e10s resolve the bug? Does dragging selected text in the url bar work as expected?

I have the same issue on ArchLinux with GTK 3.18.2. Disabling e10s does resolve the bug. There seem to be a duplicate: https://bugzilla.mozilla.org/show_bug.cgi?id=1214504