I will not go into details on why you would want to remove selected entries from your firefox history. But we are geeks, we have all sorts of dark secrets. So how would you delete selected entries from Firefox history ?
Press Ctrl+H to access your web history in the Firefox sidebar, type some characters in the search box to find the website(s) that you want to remove, right click and select the "Forget About This Site" option.
This option lets you delete either entire domains (like google.com) or even sub-domains (like images.google.com) from your browser history. If you like to selectively delete only a couple of web pages from the history (and not the entire website), just right click the web page title in the History box and select Delete This Page or hit the Del key on your keyboard.
Now, you want to clear the tracks for last few hours or few days. How would you do that ? (we are still not going into the reason of doing this)
Press Ctrl+Shift+Del in Firefox to open the "Clear Recent History" dialog and select "the last two hours" or "my history for today" option. This will delete only your recent Internet history while leaving the old data untouched . (See the screenshot below)