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Maybe your localstore.rdf is corrupted, try unhide the hidden files and folder, go to your profile folder, close firefox, delete or rename the localstore.rdf file and restart Firefox.
Try see if this happens in safe mode:
*[https://support.mozilla.org/kb/troubleshoot-firefox-issues-using-safe-mode Firefox in safe mode]
Maybe your localstore.rdf is corrupted, try unhide the hidden files and folder, go to your profile folder, close firefox, delete or rename the localstore.rdf file and restart Firefox.
*[http://kb.mozillazine.org/Show_hidden_files_and_folders]
*[https://support.mozilla.org/kb/profiles-where-firefox-stores-user-data Profiles]
Also:
*[https://support.mozilla.org/kb/reset-firefox-easily-fix-most-problems Reset Firefox]
*[https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles Create a new profile]