Broweser tab dragging suddenly triggers Mission Control after macOS update

I cannot replicate the behavior. With Drag windows to top of screen to enter Mission Control enabled, I can rearrange Firefox tabs as long as I drag them horizontally and not up to the menu bar on my Mac running Golden Gate.

If I move the tab up, especially if the window is at the top of the screen (or in full screen), then Mission Control is activated.

I suspect this is a user action error rather than a macOS problem. You can disable the feature in System Settings > Desktop & Dock.

More info: View open windows and spaces in Mission Control on Mac – Apple Support

On my Mac, that takes effect immediately. If you change the setting and it does not take effect, there may be an issue with a system extension or a corrupt preference file. See if the problem is present when you boot in safe mode. That process performs some system cleanup and clears caches, and also disables 3rd party extensions that may cause problems.

Start up your Mac in safe mode - Apple Support

If that does not correct the issue, test in a new user account. A newly-created user account will have all settings at default, and if the issue does not occur in that new account then it provides guidance on what may need to be changed to correct the issue.

Add a user or group on Mac - Apple Support

Once the testing is complete, the new account can easily be deleted.

Delete a user or group on Mac – Apple Support

Those steps will help to isolate the problem.

First, note that I do use Firefox but it is not my default browser.

I tried to reproduce the problem you are describing, but dragging horizontally works fine for me in Firefox. I have to drag upward to trigger Mission Control (as set by "Drag windows to top of screen...").

Maybe you are dragging upward, even if so slightly? Turning OFF"Drag windows to top of screen..." should immediately stop this - no need to restart, I believe.

Also I noticed that Firefox puts tabs at the very top, whereas in Safari they are further down (below the address bar) - thus it requires a longer upward move if one is to trigger MC.

Another thing: Firefox also allows you to put tabs on the side - this may be another alternative, though it looks significantly different from every other browser.

mahimahipanini wrote:

Only in Firefox, as soon as I dragged a tab to the upper left corner of the screen, close to the menu bar area, the multi-windows and spaces are triggered.

At this point, my gut feeling says this is a Firefox specific issue.

Yes, I can replicate that. With the setting to enter Mission Control by dragging windows to the Menu Bar toggled OFF, dragging a Firefox tab to the very top of the screen will still enter Mission Control, and that doesn't happen with Safari tabs.

Bugs can be reported to Apple here:

Feedback - macOS - Apple

The workaround is to rearrange your Firefox tabs by dragging them horizontally or down, instead of up.

The workaround is to

I got the exact same issue and it only seemed to happen in Firefox, and only when moving tabs in full-screen mode.

Finding this quite annoying as it disrupts my typical workflow too, I looked up my mission control settings and made sure every toggle is off, then logged out and logged in (and restarted as well), but still, the same issue is sticking around. To further trouble shoot, I tried the same steps with Safari, Chrome, Edge, and Opera, but none of them ever called out mission control. Only in Firefox, as soon as I dragged a tab to the upper left corner of the screen, close to the menu bar area, the multi-windows and spaces are triggered.

At this point, my gut feeling says this is a Firefox specific issue.