1986589 - when moving Firefox window from main monitor to extended monitor it creates 2 taskbar buttons on extended monitor

Status: NEW

(Firefox :: Shell Integration, defect)

Description

[vykng]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:142.0) Gecko/20100101 Firefox/142.0

Steps to reproduce:

Open Firefox on main monitor and slid it to extended monitor.

Actual results:

creates 2 taskbar buttons on extended monitor like there are two windows open but there is only one.

Expected results:

it should have just showed that I have the one window open in the extended desktop taskbar.

Comment 1

[vykng]

Windows 11 Home with all updates

Processor Intel(R) Core(TM) Ultra 7 265F (2.40 GHz)
Installed RAM 32.0 GB (31.7 GB usable)
System type 64-bit operating system, x64-based processor
Pen and touch No pen or touch input is available for this display

running 2 monitors chained on 1 display port

Comment 2

[BugBot [:suhaib / :marco]]

The Bugbug bot thinks this bug should belong to the 'Firefox::Shell Integration' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 3

[Robin Steuber (she/her) [:bytesized]]

Could you please include a screenshot?

Comment 4

[vykng]

Attachment: Screenshot 2025-09-04 144030.jpg

Comment 5

[darioviva]

I also have the same Bug. This was not the behaviour in Win10. I updated to Win11 three days ago, and ever since I have this problem. When having multiple tabs (and showing the title in the taskbar) the problem is even worse.

Comment 6

[darioviva]

Attachment: Screenshot 2025-09-10 203927.png

I only have one firefox window open. but the complete taskbar is full.

Comment 7

[darioviva]

they also talk about it on mozilla connect: https://connect.mozilla.org/t5/discussions/persistent-ghost-tabs-appear-on-windows-taskbar-with-dual/m-p/94213/thread-id/36732

Comment 8

[BugBot [:suhaib / :marco]]

The severity field is not set for this bug.
:dmcintosh, could you have a look please?

For more information, please visit BugBot documentation.

Comment 9

[Duncan McIntosh [:dmcintosh]]

Thanks for the report!

Thanks :darivoviva for the Connect post, I can reproduce the ghost buttons and the duplicate tab previews. However, I can't reproduce it when dragging between monitors, and I'm not completely sure whether these are the same bugs (although they at least are very related).

vykng/darioviva: A few questions to see how things are connected:

• Do you have 'Show tab previews in the Windows taskbar' enabled in Firefox's settings? (That's what I needed to reproduce it.)
• Does the bug stop happening if 'Show tab previews in the Windows taskbar' is disabled?
• If you open or close tabs after moving it, does that affect what appears in the taskbar?
• If you close the window, do the taskbar items stick around? If you close every Firefox window?
• If you move the window back, do the buttons vanish?

Comment 10

[vykng]

I don't use tabs except in certain cases but yes that setting is on.
The bug does stop if I turn that setting off.
Opening and closing tabs after moving window still produces the bug if "Show tab previews" is enabled in settings.
If you close the window nothing sticks around until you reopen it (Ghost does Not initially show up), move to main monitor ( it doesn't do it on Main monitor) and move back to extended desktop. Then the ghost is back.

Comment 11

[darioviva]

For me as well, when i turn 'Show tab previews in the Windows taskbar' it works fine. What exactly does this setting do. Seems weird that it shows tabs separatly on secondary screen but not on the main display.
Thanks for this hint though.

Comment 12

[BugBot [:suhaib / :marco]]

The severity field is not set for this bug.
:dmcintosh, could you have a look please?

For more information, please visit BugBot documentation.

Comment 13

[Duncan McIntosh [:dmcintosh]]

Thanks both of you for the help, and also for the patience!

(In reply to vykng from comment #10)

Opening and closing tabs after moving window still produces the bug if "Show tab previews" is enabled in settings.

vykng—Just to clarify, do the newly-created tabs appear in the taskbar when you make them, or do you have to move it to the main monitor and back?

If you close the window nothing sticks around until you reopen it (Ghost does Not initially show up), move to main monitor ( it doesn't do it on Main monitor) and move back to extended desktop. Then the ghost is back.

Interesting, it sounds like there's two different bugs: the one I reproduced had permanent ghost icons, and yours doesn't. I can't reproduce your bug—I can move Firefox to and from an external monitor without anything happening (with that setting enabled).

---

(In reply to darioviva from comment #11)

For me as well, when i turn 'Show tab previews in the Windows taskbar' it works fine. What exactly does this setting do. Seems weird that it shows tabs separatly on secondary screen but not on the main display.

It shows a preview of each individual tab under the taskbar icon, and overall lets you control tabs from the taskbar. Notably it's not meant to change anything on other displays. :)

darioviva—can you confirm whether the extra icons stay after closing all Firefox windows?

---

What I plan to do:

• I suspect the bugs from that Connect post are Windows bugs, especially due to Effect #1. I've filed bug 1991156 to track it on our end, and I'll contact Microsoft about it once I'm able to check that my steps are right.
• I suspect this bug is different, although I'm not able to reproduce it. Even if we could, I'd like to figure out first what to actually test with the repro.

Keeping myself needinfo'd to make sure I don't forget about this.

Comment 14

[Duncan McIntosh [:dmcintosh]]

I can reproduce this bug on a second monitor if the window opens for the first time, or it's moved onto another monitor when "When using multiple displays, show my taskbar apps on" is set to "Main taskbar and taskbar where window is open" or "Taskbar where window is open".

I think this is different than the Connect bug, since it does disappear when Firefox closes. It magically fixed itself a bit after, might try to investigate why. Setting this to S3 since this is annoying but otherwise 'just' a cosmetic issue. I'm thinking it might be a Windows bug, but I'll look into it a bit more first.

:vykng, what is that setting set to on your system?

Comment 15

[vykng]

Windows Taskbar settings: When using multiple displays, show my taskbar apps on...'Taskbar where window is open'
'Show tab previews in the Windows taskbar' is disabled in Firefox's settings.

As long as I keep the Firefox setting disabled everything is fine, so I have just been keeping this way.

Comment 16

[BugBot [:suhaib / :marco]]

Clear a needinfo that is pending on an inactive user.

Inactive users most likely will not respond; if the missing information is essential and cannot be collected another way, the bug maybe should be closed as INCOMPLETE.

For more information, please visit BugBot documentation.