Firefox on my PC seems to disagree with you. Try to use any site with a Flash video player since some of the recent updates and you're very likely to see a hang. I don't know whether the cause is Firefox or Flash, but the end result is still taking out the entire browser session, not just the tab with the Flash video.
No. Firefox's multi-process support ("Electrolysis" aka e10s) is only enabled in the Nightly channel. Firefox does not yet use tab-per-process like Chrome. Nightly only uses two processes: one from the browser (the "chrome" process) and one for all tabs (the content process). You don't get crash or security isolation between tabs when they all share one content process, but that process can be sandboxed by the OS and it reduces memory overhead. Firefox will later experiment with multiple content processes, comparing one vs N tabs per process.