If what you're saying is true, then your handful of extensions are conflicting with each other. disable one of the handful, and see if the crashes disappear. if not, disable another one.

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.