How can I recover my previously opened tabs / restore session?

Question

HI, I've been struggling the last few days to get back all the opened tabs I had in my Firefox window. My deault setting was to resume the Firefox session from where it was when I last exited Firefox. But some weird toolbar got somehow installed in my PC and when I uninstalled it all my browsing history was deleted (from all my browsers, IE, FF and chrome) and my precious Firefox tabs were gone.
These tabs are really priceless, I collected them through some months of research and it would be impossible to redo all my work. Although I managed to find some of these sites in my browing history when I restored all of it via the "restore" function in places.sqlite file properties (in the "previous versions" tab), it's impossible to find the other sites I need by checking every visited site in my browsing history, there are thousands of them and it would be the same as starting all over from scratch.
I know too that it was unbelievably stupid of me to not bookmark these sites before, but please, isn't there any way of retrieving those lost tabs? What irks me the most is the fact that the tabs weren't loaded when I opened Firefox, but only when I clicked on them, which means that I have no clue on which dates to find the tabs, since they were only visited at the time I found them, and never loaded again.
I'd be most grateful to any hint that might solve this problem. Thank you for your attention.
PS: I should mention I've already tried Window's "System Restore" but to no avail; when I open Firefox, after having a previous session restored, it will display the same tabs I left recently (as opposed to my previous tabs, that remain lost). My OS is a win7 64 bit Ultimate

Answer 1

edvardgrieg put me on the right track so thanks. Though my solution was different.
sessionrestore.js is indeed where your tabs are saved, and as you may have found out, if you lose your tabs this information is overwritten in the sessionrestore.js file.
I am using Windows XP and so I did not have the Previous versions option described by edvardgrieg. What I did have was a couple of backups of the sessionrestore.js file. One was called sessionrestore.bak and the other sessionstore.bak-20131112160018 (the long number being the date it was made). So I merely removed sessionrestore.js and renamed my sessionstore.bak-20131112160018 backup to sessionrestore.js. Remember to close your browser before you do this otherwise your newly restored backup will be overwritten and your tabs lost forever, so back up the backup like I did before you do this.
I also had a few months worth of tabs (approx 150). Glad to get them back.