Firefox 'solves' this by only loading tabs that have been given the focus upon auto-restart. So, if you have 10 tabs opened, and your computer restarts and Firefox is opened, the only tab that will actually load is the one that was last active.
I don't like this. It just feels like Firefox is being lazy to me. I notice I have to wait a second or two when I switch to another tab. This is annoying because I remember seeing the page load before I restarted. My subconscious doesn't realize that it was a different process. I'd rather my browser and everything else involved work a little harder to give me the illusion that nothing has changed after I restart.
Also frequently FireFox crashes for me are due to it hitting the 4GB memory limit (well closer to 2GB obviously), so restoring all tabs would just result in Firefox crashing again. Restoring them piece meal lets me close down ones I do not need, thus allowing me to get FF's memory usage down to acceptable size.