I wouldn't write off an excellent browser due to this issue. It almost has to be something on your end as noone else seems to having this issue. Not completely sure I follow you on your problem. You type an address in to the address bar and then hit enter but nothing happens? Is that right?
Try uninstalling it completely, run ccleaner doing a registry clean, restart and install it again, then restart again before using firefox again. Alot of restarts i know lol but if it gets the job done ...
I am running Microsoft Security Essentials and have been for a while now without any issue.