Hi, please Troubleshoot Firefox issues using Safe Mode . Scan your PC with malware removal software.

Let me know if it is working.

I already tried to open Firefox in Safe Mode which didn't fix the problem. I'll run a malware scan and see if that works. Thanks for the quick response!

try to disable/remove unwanted addons or toolbars. clear you browsing cache. and restart your firefox.

let me know if it works.

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

If the 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

Looks like it was some kind of malware after all. Problem solved - thanks guys!