do i have to click 'sync now' as final step? nope, no change. i log out and try to log in with other email just to be sure i get warning: all bookmarks etc will merge to new login, got zero to lose so 'ok'. no change. click 'sync now' no change.

log out and into other account, sync now, nothing works. closed ff, renamed old folder to new name, that didnt work. how do i get my add-ons and last session tabs back?

I don't know why Sync isn't restoring all of your data. Did you get bookmarks back eventually? Sync definitely may take time.

What does this mean -- what folder:

wolf said

renamed old folder to new name, that didnt work.

When you did the Reset, did you instruct Windows to preserve your data? That could be either "in place" or in a C:\Windows.old folder (a temporary folder kept for 28 days).

If you see a C:\Windows.old folder, before exploring further, please turn on viewing of hidden files and folders:

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

Then try to find:

C:\Windows.old\Users\your-user-name\AppData\Roaming\Mozilla\Firefox\Profiles

Do you have anything there?

Note: when experimenting, always copy/paste and don't move the old files.