Sounds like the shortcut file that opens Firefox was deleted somehow.

Try pinning Firefox to the taskbar again through the start menu:

1. Press the Windows Key to open the start menu
2. Type Firefox to search for the application
3. Right-click on the Firefox icon
4. Click Pin to Taskbar (this may be located under More)

Hi, Thanks for the quick response. The above did not change the issue. Windows "cannot find" the "firefox.exe" file, even if I go to the folder it's in and click on it. I think I know how I did this. CCleaner kept asking me to put Firefox to sleep (stop running it in the background). I have always ignored this in the past. The new CCleaner does not have the ignore button. I snoozed it. Then, every time I open CCleaner, the screen dims and the "do you want this program to make changes to your device" window opens. Something in CCleaner is not working. So, I uninstalled it again. Should have disabled the Firefox sleep first. Maybe I'll reinstall CCleaner and see if I can change the sleep function?? I don't want to reinstall Firefox because I'll lose my bookmarks.

That's strange, you're not able to launch firefox.exe even by navigating to it in File Explorer?

If you can't undo whatever CCleaner has done, you should be okay to uninstall Firefox and reinstall it. Firefox doesn't remove your profile when uninstalling itself, so you shouldn't lose bookmarks and passwords after a reinstall.