Enter button not present on History library window.
Your instructions for the following can be quoted:
Clearing all items for a single site
At the top of the Firefox window, click on the Firefox button, go over to the History menu (on Windows XP, click on the History menu), and select Show All History to open the Library window. At the top right corner, type the name of the website you wish to forget in the Search History field, and press Enter. In the resulting list, right-click on the site you wish to forget, and select Forget About This Site. NOTE: Using Forget About This Site will remove all traces of that site from your History. For more information, see Clear Recent History. Close the Library window.
The problem is, there IS NO ENTER button. I'm on Windows XP with the newest Firefox browser. Trying to use my key board enter key also does not work. Pretty hard to do this when such a feature is literally missing
Opaite Mbohovái (1)
It shouldn't be necessary to press the Enter key or do any other action.
If you enter the text in the search bar then Firefox should start the search automatically.
If you click the clear button at the far right of the search bar then you should see all history entries.
If that doesn't work then check for problems with the places.sqlite database file.