If you want to fully remove the old mozilla, you will have to un-install it.
In the menu, System Settings -> Add/Remove Applications
You can also remove it manually. To get a list of all RPMs with the word mozilla
rpm -qa | grep mozilla
Using the list, remove the old RPMs with the following syntax:
rpm -e package_name
To edit the menu, right-click on the menu icon (the red hat) and select Menu Editor.