2004139 - tab selection and or preview does not work when the cursor is on the top-most part of a tab selection area on maximized window

Status: RESOLVED DUPLICATE of bug 2004018

(Firefox :: Tabbed Browser, defect)

Description

[[e-mail]]

Attachment: Bugged behavior.

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:146.0) Gecko/20100101 Firefox/146.0

Steps to reproduce:

the bug described bellow only affects the behavior when the cursor is on the top-most part of the window, when you have the window maximized.

if the window is not maximized you cannot click due to the cursor changing to allow you to resize the window and "forcing" you to interact within the rounded frame limits of the tab, where the behavior is not bugged.

on previous firefox versions you could hover / select a tab by clicking above the framing of the tab as if you were clicking on the top-most part of the tab, or as if your cursor was clicking on the "edge of the screen" - when you have the window maximized.

this is convenient, you could simply click on the general tab area and did not need to click within the rounded frame limits of the tab.

this is no longer the case.

Actual results:

1. if you have multiple pinned tabs, and you hover and / or try to select a tab
   with the left mouse button and the cursor is on the top-most part of the tab / window, the selection and tab preview do not happen (the preview is inconsistent).

there are inconsistent tab previews and no tab selection happen
when the cursor is on the top-most part of the tab / window - when you have the window maximized.

this only changes starting on the four last tabs of a list of various opened tabs, in which case the hovering / selecting behavior is normal for the four last tabs, and bugged to the remaining.

See the attached two videos.
One shows normal behavior for hovering / preview first, then selections;
Second videos shows bugged behavior for hovering / preview first, then selections.

2. an alternate behavior also happened with no pinned tabs.

i had about six tabs open; i could not select the left-most(first) tab with the left mouse button while the cursor was on the top-most part of the tab / window (as i described above)

but this bad behavior - mis-selection / hovering and no preview - only happened if the cursor was hovering over the middle part of the left-most(first) tab frame,
and anywhere towards the right part of the left-most(first) tab frame

The tabs following the left-most(first) - the second, third, etc - could be selected / hovered previewed as normal.

See attached image.
But the image is just a visual aid since i can now longer make it happen
and i did not make a video out of it.

Expected results:

when the window is maximized and the cursor is on the top-most part of the tab selector rounded frame, tabs should still show their previews and be able to get selected be they pinned or not.

Comment 1

[[e-mail]]

Attachment: Correct behavior.

Comment 2

[[e-mail]]

Attachment: Hard to reproduce, related bug.

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

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

Comment 4

[[e-mail]]

Comment on attachment 9530957 [details]
Bugged behavior.

wrong codec

Comment 5

[[e-mail]]

Comment on attachment 9530958 [details]
Correct behavior.

wrong codec

Comment 6

[[e-mail]]

Attachment: Bugged Behavior.

Comment 7

[[e-mail]]

Attachment: Correct Behavior.

Comment 8

[[e-mail]]

Attachment: Hard to reproduce, related bug.

Comment 9

[[e-mail]]

i should also emphasize that i tested this on a new profile without extensions...

so far, this only seems to be present on the most current 146.0 version.

not even 146 beta 9 has this bug.

Comment 10

[[e-mail]]

when i reported this i was using firefox 146.0 release candidate build 1 from december, 2, 2025

i just tested firefox 146.0 release candidate build 2 from december, 5, 2025

the behavior changed...

i pinned about 6 blank new tabs, plus i had about 8 un-pinned blank tabs with two other tabs at the end with youtube pages.

now i can select them if i click them, with the cursor being above the rounded tab frames
but still no previews...

so, half the problem still persists...

and this bug only seem to show up after i have open some random urls, then close them, and then, open various empty tabs...

Comment 11

[Andrew S.]

There are similar closed bugs that I cannot comment in.

According to https://www.firefox.com/en-US/firefox/147.0beta/releasenotes/ , the behavior preventing tab selection in top corner was fixed, however in my Beta 147.0b1 I still cannot select tabs by clicking top-left corner. Clean profile has the same thing.

Comment 12

[Mathew Hodson]

This could be the same as bug 2004018 which was fixed in 147.0b3. Check if that fixes it for you.

Comment 13

[Dão Gottwald [:dao]]

(In reply to Andrew S. from comment #11)

There are similar closed bugs that I cannot comment in.

According to https://www.firefox.com/en-US/firefox/147.0beta/releasenotes/ , the behavior preventing tab selection in top corner was fixed, however in my Beta 147.0b1 I still cannot select tabs by clicking top-left corner. Clean profile has the same thing.

Could you please check in 147.0b3? Thanks!

Comment 14

[Andrew S.]

Not sure where to get 147.0b3 as it is not available on https://ftp.mozilla.org/pub/firefox/releases/ and 147.0b2 (the one that I have) still has this issue.

Comment 15

[Andrew S.]

Updated today to 147.0b3 and seems like this issue is fixed now.