Windows 7 taskbar thumbnails seem flakey for Firefox. They are frequently all blank, and show a lot of leftover tabs.

Question

I'm running Firefox 3.64 on Windows 7. When I hover my mouse over the FF icon in the taskbar, it shows a bunch of thumbnails that are blank except for a "waiting" icon (I use the circle rather than the hourglass.) There are frequently a lot more thumbnails than I have open tabs, so I assume some of them are leftovers. I seem to have to shut down FF from the Task Manager to get rid of the extras.
== This happened ==
Not sure how often
== I started using Win7 I guess

Answer 1

(1) Firefox's built-in post-crash page has not been a real HTML page for a long time (for example, from the time of Firefox 22, see: [https://support.mozilla.org/en-US/questions/968212 Want to save LOTS of versions of "Restore Session.xht" from the "oops ..." page for later use]). If you had this working differently with Firefox 25, that might have been created by an extension.
You can check to see whether extensions are disabled or need an update on the Add-ons page. Either:
* Ctrl+Shift+a
* orange Firefox button (or Tools menu) > Add-ons
In the left column, click Extensions. The disabled extensions cluster toward the bottom of the list. To poll for updates, use the "gear" button above the list and choose Check for Updates.
If you used the Reset feature (or Firefox automatically did a reset due to some problem during upgrading), you will need to reinstall missing extensions. The reset feature creates a folder on the desktop named Old Firefox Data. Do you have that folder? There may be data you can recover from it.
(2) There are many ways for history to get cleared, both internal to Firefox and external. Could you double-check your Privacy settings?
orange Firefox button (or Tools menu) > Options > Privacy
* The "Firefox will" drop-down says Remember History: Firefox shouldn't be clearing history, but an add-on or external software could do it
* The "Firefox will" drop-down says Use custom settings for history: inspect the "Clear history when Firefox closes" setting to make Firefox isn't set to clear history. Also check your add-ons and consider external software.
Firefox normally accumulates months of history. However, some of Firefox's database sizes are based on disk space available. If your hard drive is very full, Firefox might reduce the amount of history stored.