Hi Keorl, You can easily restore your bookmarks on your work computer. Firefox does a back-up of your bookmarks every day - automatically. See this article for the How To: Restore bookmarks from backup

Keorl, As far as I know, History, Extensions, etc. can be recovered from an "old" profile: Recovering important data from an old profile if one is available.

Hi Keorl, for everything else other than bookmarks, I realize that is a disaster. As far as I can tell, that "remove data" feature was intended for when you accidentally used Sync on a public PC (like at your local library) and not a PC you use regularly. More warnings may be needed.

Meanwhile, I suspect everything is going to transfer to your home computer, so while I do suggest making a quick backup of the home computer before letting Firefox reconnect -- see: Back up and restore information in Firefox profiles -- you may end up with your missing work history, etc., at home and then there might be some options for transferring it back, although now that it's mixed up, not very easily.

Does your office make local backups of your computers? The critical folder is your profile folder: Profiles - Where Firefox stores your bookmarks, passwords and other user data.

Windows 10 may have created a shadow copy of your profile folder at the last system update. Please do not use System Restore -- that usually makes things worse -- but what you would do is scour the latest restore point for files to use for recovery. Your IT policies might restrict installing these programs, but here are the details:

Finding/Using Shadow Copies

You can use a utility program to search inside restore points to try to locate a recent file that's usable. (Please do NOT try to use the built-in Windows System Restore for this because you would lose too much data.) Here are the steps:

(1) Set Windows to show hidden files and folders:

https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

(2) Download and run one of these two programs:

• System Restore Explorer: http://nicbedford.co.uk/software/systemrestoreexplorer/
• ShadowExplorer: http://www.shadowexplorer.com/

Within the most recent restore point shown in the program, you can explore along this path to see whether you can find a shadow copy of your profile:

\Users\your-user-name\AppData\Roaming\Mozilla\Firefox\Profiles\

(3) Two things to check:

You can export the entire profile folder (names are somewhat like ab12cd34.default) to your currently live desktop or documents folder.

Anything useful?

Next step would be: Recover important data from an old profile

Thank you for your answers :)

What I did is reconnect to sync and remove all home bookmarks as well as some history. Now I'm still out of quite a few things like tampermonkey scripts, ff theme ... .. I don't have an old profile unfortunately : I looked everywhere for the one I saved from my old work computer (which was changed a few months ago) but apparently I deleted that zip after using it to set up this computer, and the usb stick was encrypted/rewritten in the meantime so Recuva doesn't help.

I'll try to find shadow copy of ff profile later today, it sounds promissing. If I can find one I'll just save the current not-ideal one and replace it with the old version.