Hi
riknetwork,
Thanks for providing the information that a newly installed utility was used directly before the problem appeared for you.
Good detective work.

It may not be the actual cause of the problem, but it is one aspect of problem-solving that some folks overlook.
A comment about "duplicate removal" utilities…………
Any ordinary computer is bound to have dozens and maybe hundreds of duplicate files stashed around in important locations in the operating system and the program files directories, where various applications typically "look for" the file needed to complete their function. It is not always a good thing to remove such duplicates.
The kinds of "duplicates" that may be useful to remove would be duplicate entries of the same document or photo or song that is taking up space but not providing a necessary function. Unhappily, duplicate-removing-utilities will generally display lists of "all" duplicates, and the less familiar owner/user may incorrectly believe that they are safe to remove. <– not always the case.
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Since the previously suggested fixes didn't help, you may benefit from the following:
You may have installed an add-on/extension that is causing your difficulty:
Open FireFox in Safe Mode. Extensions won't be loaded and you can disable various extensions/add-ons
1. Click Start button
2. All programs
3. Mozilla Firefox
4. Mozilla Firefox (safe mode)
5. Use the Firefox Safe Mode option panel that appears before Firefox continues to boot.
—- complete any changes/removal of add-ons and/or select Reset all user preferences to Firefox defaults
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If the above does not resolve your problem, you'll need to Uninstall/Reinstall Firefox
But first……… You may want to save your Bookmarks
1. Click the Bookmarks menu.
2. Manage Bookmarks.
3. In the new window click File and then Export.
4. Select the name for your bookmarks and you are done.
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Having already backed up your Bookmarks (or not) you are ready to Uninstall/Reinstall Firefox
– Use Control Panel - Add/Remove Programs to uninstall FireFox
– Use Internet Explorer to access the Mozilla Firefox website and install the latest version of Firefox from that site.
If you continue to have difficulty, please start a New Topic, so that we don't lose your specific problem or get it confused with other questions and solutions specific to the original poster of this present Topic.
If the above steps resolve your problem, please post back into this same Topic thread with confirmation that the problem got resolved.
I look forward to seeing you around the Forums.
Lots to read and learn. Enjoy
Best Regards