Most people don't open a lot of windows and tabs at the same time.
Define many. I routiney have 10+ windows with 20+ tabs in most of them, and another 10+ windows with 1 or 2 tabs.
I do software development; not primarily web based, but it comes up both in web apps and web services, so I'm regularly loading and debugging sites that are rendering pretty broken stuff too.
I honestly can't recall the last time FF crashed on me for any reason.
The problem is much worse when many windows and tabs are open under the Windows OS and Windows is hibernated several times.
I haven't rebooted my Mac in ages -- last time I installed an update that needed a reboot. A few months easy.
My home office win 7 destkop gets rebooted around once a month for windows updates. Sleep/hibernate/wakeups the rest of the time.
I'm not disputing your experience. But I do wonder whether your crashes are tied to a particular plugin, or are linked to some other characteristic of your system. We use FF at the office as well, on dozens of computers -- stability is NOT problem there as well. Don't know what to tell you.