https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings
What does the refresh feature do?
All of your Firefox settings and personal information are stored in a
profile folder. The refresh feature works by creating a new profile folder for you while saving your important data.
Add-ons which are normally stored inside the Firefox profile folder, such as
extensions and
themes, will be removed. Add-ons stored in other locations, such as
plugins, will not be removed but any modified preferences (such as plugins you have disabled) will be reset.
Firefox will save these items:
- Bookmarks
- Browsing history
- Passwords
- Open windows, tabs and tab groups
- Cookies
- Web form auto-fill information
- Personal dictionary
These items and settings will be removed:
- Extensions and themes, website permissions, modified preferences, added search engines, download history, DOM storage, security certificate and device settings, download actions, plugin settings, toolbar customizations, user styles and social features will be removed.
Note: Your old Firefox profile will be placed on your desktop in a folder named "Old Firefox Data". If the refresh didn't fix your problem you can restore some of the information not saved by
copying files to the new profile that was created. If you don't need this folder any longer, you should delete it as it contains sensitive information.