P.S. - I had also done a Time Machine before the format, but weirdly the Firefox folder inside Library --> Application Support, wasn't included in the backup... So no way of recovering my profile...

BTW am using Linux not Apple and am NON-Technical.

As long as you set Sync up using the same email address and the same password, it seems to work.

When install updated OS, then log into Sync using same email and password, it takes Sync a while for Firefox to sort everything out.

Using Firefox 36.0 then using History then Tabs from other Devices am seeing there some Tab changes (not sure what this is yet) , at least know is accessing shared records.

 - - - - 

Sync records around every 10 minutes a copy, sometimes when first log in it takes almost as long to (copy back to ? ) access on this computer all the recorded details.

Sync may record a lot of unnecessary things, whether this slows down access to the essential records am not sure.

Sync account records sync-actions approx every 10 minutes from when sync is started till Sync ends.

my record is stored :

(path = ) /home/username/.mozilla/firefox/DELETED.default/weave/logs/error-1426030647838.txt

Sample Linux command: cat -n /home/username/.mozilla/firefox/DELETED.default/weave/logs/error-1426030647838.txt

(using -n am able to see in this file 312 lines, then after next log file shows, see fewer lines recorded. )

Try using your terminal/prompt command to read your Sinc record file :-)

Paul, thanks for your help... but I have no idea how to do that Terminal command or even what to do with it afterwards... I'm no expert... I just wanted my tabs! :)

I'm accepting it as a lost cause by now... Next time, I'll rely on a session manager or something...