Affected versions

• 78.0ESR, 81.0, 82.0a1(2020-09-20)

Affected platforms

• macOS 11.0 (20A5364e), macOS 10.15;

Steps to reproduce

1. Launch Firefox, open 2-3 tabs;
2. Drag any tab so it would open in a separate browser;

Expected result

• new window/tab opens almost instantly;

Actual result

• delayed action after mouse-button release;

Regression range

• not a regression, visible after updating the OS to 11.0(20A5364e) from public beta3;

Additional notes

• attached recording with the issue;
• not affecting macOS 10.13.6;
• S3 suggested severity since it appears to be manifesting as bad only on certain devices, ex: MacBook Pro (13-inch, 2017, Four Thunderbolt 3 ports).

Attaching browser about:support data as well.

Are you able to reproduce this in macOS 11 Beta 7 (build 20A5374g)? You've got Beta 6 (aka Public Beta 3).

(In reply to Steven Michaud [:smichaud] (Retired) from comment #2)

Are you able to reproduce this in macOS 11 Beta 7 (build 20A5374g)? You've got Beta 6 (aka Public Beta 3).

Please let us know if you can reproduce this on Beta 7. The problem you're hitting might be the same as bug 1663467 which was fixed in Beta 7.

Need to wait for the public release(s), will keep an eye on this on the next update.

Just got updated to 20A5374i (Beta 8) and I can still see the delay up.

Noticing a somewhat odd behaviour as well.

Dragging the lone tab-window around appears to teleport the browser in a pre-set and offset position close to the initial-main window.

This problem is reproducible for me on macOS 10.15 Catalina (both the description in comment 0 and the issue on comment 6). While we try to improve this, the bug doesn't need to block macOS 11 support. In my case, the delay when moving a tab out of the window was similar compared to on 10.15. Cristian, please update the bug if that is not the case.

You are right, just confirmed on a machine with 10.15.6 as well.
The behavior is the same, as opposed to what I noticed on 10.13 when filing the report; for both the description and scenario on comment 6.
Indeed, it's not a blocker for macOS 11, thank you for the input.

This bug also exists on macOS 12.

I wonder to what degree bug 1635761 has helped here. Can someone re-test? If there is still a noticeable delay, can someone record a profile with the Firefox profiler?

(In reply to :Gijs (he/him) from comment #11)

I wonder to what degree bug 1635761 has helped here. Can someone re-test? If there is still a noticeable delay, can someone record a profile with the Firefox profiler?

It's all good for me. I can move a little the tab but It still detaches as expected. For me, It's fixed.