I too get past 50 tabs.
But that's spread across many windows.
I haven't found a good way to save all windows and tabs (for reading later) so that I can shutdown a PC.
The best I can come up with is to end the process in task manager, and with firefox only having 1 process it's great.
Next time I run firefox it tells me it wasn't shutdown and if I would like to restore the last pages, which I do and bam all my windows and tabs are back.
Now if MS can fix hibernation to work properly with desktops it would help.
Works like a champ on my laptop.