User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:94.0) Gecko/20100101 Firefox/94.0

Steps to reproduce:

On Ubuntu 16.04 - I have found many times over that more often than not, dragging a tab with the mouse to move it to its own new window causes problems.

Actual results:

After dragging, the tab does not move to its own window but returns to the parent. Furthermore, for the rest of my session, there is always at least one tab (the last tab interacted with with the mouse) that does not respond to mouse clicks, almost as if the tab is gone. The "X" button does not darken when the mouse hovers over it, right-clicking the tab yields no tab-related dialogue, just the same dialogue as if the window was right-clicked without a tab. Further, no more tabs can be dragged around with the mouse, the search bar doesn't respond to clicks, and the back, forward, and refresh buttons also don't respond.

All of the functionality lost in these episodes is still accessible by way of keyboard shortcuts, as far as I can tell.

Expected results:

The tab dragged out of the window should create their own new window, and everything should remain responsive. Everything goes as expected about 10% of the time, and I find dragging the tab very slowly raises the chances.

The Bugbug bot thinks this bug should belong to the 'Core::Widget: Gtk' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Can you please test latest nightly? How-to is here:
https://fedoraproject.org/wiki/How_to_debug_Firefox_problems?rd=Bug_info_Firefox#Testing_Mozilla_binaries
Thanks.