That behaviour is typically caused by an add-on or conflicting add-ons. Try the procedures in the [[Troubleshooting extensions and themes]] article.

Still having problems

Try creating a new profile. This will establish if the problem is caused by something in your profile (location where user data/settings are stored) See [http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows Creating a new Firefox profile on Windows] If the new profile works, you can transfer data such as bookmarks and passwords to the new profile. It is best not to transfer the preferences file, as you issue may be related to a preference. You should also re-install the add-ons rather than trying to copy them. See [http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox Transferring data to a new profile].