To fix the problems such as slowness and other issues Firefox users face, Mozilla has introduced Refresh feature, which is also useful to remove malicious toolbars and restore search engine defaults, you can find the Refresh button in the about:support page.
After refreshing Firefox, you’ll find “old Firefox Data” folder on your desktop. Mozilla’s intention behind this is to let you restore your old profile data if you didn’t find much help with the newly created profile.
And more over, you can restore all lost customization including add-ons, without needing to install them again using this folder, but how is the question? We’re explaining that below with step by step in detail.
Restoring data from old profile folder on desktop after refresh, to Firefox browser
1. Ensure Firefox is not running , backup current Profile folder using tools like Firefox backup tool or MozBackup or you can manually copy Profile folder- click on “open Folder” in the about:support page -and paste to another location in the the hard drive.
2. Open Old Firefox Data folder and profile folder after that, and copy all files in it with Ctrl +C button, now launch Firefox and open profile folder by visiting about:support page and close Firefox browser after that.
3. Now use Ctrl+V to paste items copied earlier to Firefox default profile folder, when Windows Explorer shows “confirm folder replace” dialog, at the bottom of it select “Do this for all Current items” (check the screenshot below) and click “Yes” button.
5. Next ‘Copy File’ dialog appears on screen with message “there is already a file with the same name in this location, select ‘Do this for next (number shown) conflicts’ at the bottom, and click on ‘copy and replace’.
If you want to restore specific files from your Firefox old Profile to- such as bookmarks or browsing history or cookies or passwords or site specific preferences – to refreshed Firefox, please check this article from Mozilla.