I installed AVG’s latest free anti-virus software, including browser plug-ins. Shortly thereafter my Enter key stopped working when trying to type in a URL. I didn’t know AVG was the issue – I tried using other browsers (they all worked) but Firefox has all my web development toolbars and bookmarks – it’s annoying to use anything else except for testing. After searching online, I figured it out. Just uninstall or disable the plug-in and you should be fine.