Try to reset the preferences. *http://kb.mozillazine.org/Resetting_preferences *https://support.mozilla.org/kb/Resetting+preferences ---- You can also try to delete the downloads.sqlite file in the Firefox Profile Folder See: * http://kb.mozillazine.org/Unable_to_save_or_download_files#Manually_delete_download_history You can use this button to go to the Firefox profile folder: *Help > Troubleshooting Information > Profile Directory: Open Containing Folder ----- 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