[Affected versions]: - Firefox 62.0 - beta 63.0b10 - Nightly 64.0a1 [Affected platforms]: - Windows 10 x64 - macOS 10.13 - Ubuntu 16.04 x64 [Steps to reproduce]: 1. Open Firefox. 2. Open so many new tabs that the overflow is activated on the tab bar. 3. Holding your cursor in one place close the tabs so that are only about four or five. 4. Observe the tabs. [Expected result]: - After resize the close button "x" is displayed on each tab. [Actual result]: - After resize the close button "x" is displayed only on the focused tab. This behaviour is corrected after one more tab is closed. [Regression range]: This is a really old regression. What I could find was that: - first bad: 2011-04-13 - last good: 2011-04-09 I will try to find a more accurate regression. [Additional notes]: - Please looked at the attached gif to see the issue.

this is a implementation bug of Bug 465086

range https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=a174b86200d6&tochange=6bcaec19d09e

I am inclined to believe that the fix to bug 465086 caused this issue to be noticed, but I don't think it's the root problem. Before the fix, when a tab was closed, the others were "refreshed" and resized automatically and the issue couldn't be seen.