Go to about:config and in the search box type browser.tabs.hoverPreview.enabled. That will then appear below with the word true next to it. Double-click true and it will change to false.

There is also a setting called browser.tabs.hoverPreview.showThumbnails which you can also change to false but I haven't found it necessary to as it only seems to do anything if the first one is true.

I did both, but the problem, is that after I x out of Firefox, and open it again, the windows are back, and the setting is back to true. False is not locking in. I tried clicking the reset button, doesn't do any good. It's not locking in.

There's also a checkbox for this on the Settings page, last item under Tabs (which is the second section on the General panel).

If preference changes do not stick, could you check the diagnostic list in the following article: How to fix preferences that won't save.

Looks like it locked in on its own. Don't know why there was a delay.

FWIW, that box under tabs was not checked. So I don't know how this setting changed all by itself.

I thought this feature was just in Nightly because I'm not seeing in Linux in 129.0.2. see screenshot It appears to be in Windows. I haven't been over there in awhile.

The checkbox in "Settings -> General -> Tabs" only toggles browser.tabs.hoverPreview.showThumbnails, so you still see the two line title and URL.

I spoke to soon, setting is back to "true" and the windows are back.

There's three things that could be shown when you hover over a tab: 1 - in a narrow white rectangle field, you get the web address, 2 - you get a window with a picture of the page, or 3 - in a window bigger then #1 but smaller then #3, you get the name of the web site in bold, and under that the web address, not the full web address, but the address of the site the page is coming from.

I think I always got #1, I don't remember now. But never got 2 or 3.

There's three things that could be shown when you hover over a tab: 1 - in a narrow white rectangle field, you get the web address, 2 - you get a window with a picture of the page, or 3 - in a window bigger then #1 but smaller then #3, you get the name of the web site in bold, and under that the web address, not the full web address, but the address of the site the page is coming from.

In pictures -

Both are sent to false. The problem is that the "false" does not lock in. It keeps reverting back to 'true." And "show tabs in preview task bar" is not checked.

The Taskbar setting ("Show tab previews in the Windows taskbar") refers to whether Firefox shows one entry per window on the Windows Taskbar, or one entry for every single tab in every window. Very different setting.

The tab preview thumbnail ("Show an image preview when you hover on a tab") may have been enabled by a "study," which is a method Mozilla users to roll out new Firefox features gradually between updates. To check on your Firefox's active studies, you can type or paste about:studies in the address bar and press Enter to load the list. Mine lists:

Tab Hover Preview Release Rollout • Complete

at the top of a really long list. Presumably yours does, too. So there's no reason for that to re-run unless somehow Firefox is losing track of the fact that it already implemented the study, and does it again. I don't know what could cause that, unless some process is clearing the studies list so Firefox runs all the current ones again?

J, Nice pick up.

In that page that lists all the studies, there is a button up top that takes you to your settings that allowed you to opt-in to the studies. I have no idea why that was checked, I wouldn't have checked it. So I unchecked it, and it looks like the tab ID's have disappeared!

Thanks a lot!