There are two Boolean (true/false) prefs in about:config to control what to show when you hover a tab. One pref controls whether to enable this new hover feature or only show the legacy tooltip with the title.

• browser.tabs.hoverPreview.enabled

Another pref controls whether to show a thumbnail or a two line tooltip with title and URL.

• browser.tabs.hoverPreview.showThumbnails

The latter can be controlled via "Settings -> General -> Tabs".

You can double-click a Boolean enabled pref that is true to change its value to false to disable this feature.

This is the state of the settings you mentioned:

browser.tabs.hoverPreview.enabled true browser.tabs.hoverPreview.showThumbnails true

These seem to be correct. What do we need to do next?

That should make the two0line tooltip visible when you hover the tab.

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click "Refresh Firefox" in the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Here is what I have tried:

Your suggestion that it might be an add-on made me look to see if I had any. I had not explicitly installed any on my new build Windows 11 machine. But I found one installed, I believe because of syncing with my old Windows 10 machine. It was Tab Mix-Links. In the past I used Tab Mix Plus when It was required to restart with the tabs you had the last time Firefox was up or to recover tabs after a crash. I removed it on this and my Windows 10 machine and restarted Firefox. This fixed the problem on the Windows 10 machine; but not my new Windows 11 Home machine. However the Windows 11 machine takes longer to fail.

Then on my Windows 11 machine, I tried your advice to Clear cache, cookies, and history. I restarted Firefox but it still fails.

Then tried your advice to refresh Firefox and restart; but it still fails.

Then I turned off hover tab preview leaving only descriptions and restarted; but it still fails.

Then I backed up to Firefox Version 128.0.3. This works; but it is not as convincing as I would like since you must change profiles and lose all your tabs when you backup this far.

For my next test I am going to install Firefox Version 130.0 move the current profile forward to it.

               Michel

You can try "Clear the startup cache..." in "Help -> More Troubleshooting Information" (about:support).

• https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox

I tried 3 things and here is what happened:

1) I moved the new profile that worked in Version 128.0.3 forward to version 130.0 and after a while it failed.

2) I cleared the Startup Cache and after a while it failed again.

3) Then I cleared the Cache and Cookies and after that I cleared the Startup Cache. After a while it failed again as it it has been doing.

Is there a circular trace I can enable so we can see what is happening by looking at the trace right after it fails?

                    Michel