First I have to ask, why Firefox 15? Most of the volunteers here run the current version, so it's often very difficult to replicate and debug problems in old versions. Can you update? I recall (in a rather vague way) that some add-ons have created problems with the address bar. To test that possibility, try disabling ALL nonessential or unrecognized extensions on this page: Tools menu > Add-ons > Extensions category After restarting Firefox, do you notice this problem continuing or is it gone?