Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

• https://support.mozilla.org/kb/Basic+Troubleshooting#w_8-make-a-new-profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If that new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

See:

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

lockPref("toolkit.telemetry.prompted", true) is a possible source of this error, too. Tested with FF 9.0.1, the parameter seems to be no longer boolean, but integer.

Yes, the toolkit.telemetry.prompted pref is an integer in Firefox 9+

So you need to change it to:

lockPref("toolkit.telemetry.prompted", 2);