Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. Reinstall with Current Release Firefox 57.0.4 with a Full Version Installer *https://www.mozilla.org/firefox/all/ Note if your Profile is damaged you may need to create another : *https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles Please let us know if this solved your issue or if need further assistance.