User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:83.0) Gecko/20100101 Firefox/83.0

Steps to reproduce:

1. Install the extension https://addons.mozilla.org/pl/firefox/addon/bookmarks-manager-and-viewer/ and enable sidebar with this extension panel
2. Open YT - for example https://www.youtube.com/watch?v=mLrNPHn3Thc
3. Grab the player's slider on the YT
4. Drag the slider to the beginning of the movie - a little too far - so that you release the cursor over the sidebar.

Actual results:

Jams cursor position mousedown and still moves the slider YT player, even though the mouse button is released.

You can see it in the attached video.

This was a bug in Firefox for as long as I can remember.

The same thing happens if you grab and drag the Google Map (https://www.google.com/maps) too far and release the button above the sidebar.

Expected results:

The cursor should not get stuck in the mousedown position.

Thanks for reporting this bug!
This looks like a duplicate of bug 1571946 which should be fixed by bug 1680405.
Łukasz, could you try if you still see this in Firefox Nightly? Thanks.

(In reply to Edgar Chen [:edgar] from comment #2)

Thanks for reporting this bug!
This looks like a duplicate of bug 1571946 which should be fixed by bug 1680405.
Łukasz, could you try if you still see this in Firefox Nightly? Thanks.

Yes, Firefox Nightly works fine.
This problem disappears in Firefox Nightly.

(Interesting case, you fixed it right now, recently. : D)

(In reply to Łukasz from comment #3)

Yes, Firefox Nightly works fine.
This problem disappears in Firefox Nightly.

Thanks for verifying, then the fix will be included in the next release (86). :)
Close as a duplicate of bug 1680405.