Hi, seems some code has been clipped or corrupted or packet loss in a update. Please : Create a new profile as a TEST to check if your current profile is causing the problem.

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem. Never work with original files.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

After saving your date can always also : Reinstall with Current Release Firefox 59.0.1 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

Firefox immediately starts downloading the file in the background and saves the .part file to the temp folder and doesn't wait until you specify the name and the location (destination folder). If the file stays in the temp folder then it is possible that your security software is blocking the file and prevents Firefox from moving the file to the specified destination folder and rename the file to the correct file extension.