Finally! Just like Google Chrome and Internet Explorer 8, Firefox will be making each opened tab a separate process which makes things much more stable and will make use of multi-processor systems.
What does this mean for you? In theory, no more browser crashing. Instead, each tab would handle the crash instead. It’s great because you won’t lose your other opened tabs and you can always fire up another tab if something isn’t working quite right.
When will we get it? The wiki outline says a rough "bootstrap," with a non-Firefox browser operating the browser "chrome" (interface) and a single tab as separate processes, is scheduled by July 15 of this year. Phase TWO, "Parallel Improvements," would further the work on safely connecting the browser chrome to content, and is estimated for Nov. 1, 2009. Extensions, performance optimization, and multi-process content aren't even on a rough roadmap yet, so it probably won’t be this year.
So I guess it’s better late than never
(via Mozilla Links)