Considering extensions are the #2 reason (behind Flash) that Firefox crashes/beachballs, perhaps one would be wise to audit the (presumably) tons of extensions they have installed locally, to see if they conflict with other extensions?
currently using a netbook with an Atom N570. I appreciate under-powered computing. Firefox runs fine here with 5 extensions (two of which are for web development). 17 tabs are using 214.52 MB of memory. haven't had a crash or hang in a long time.