Hmm thinking about it, maybe it does not run the updated code. Ah, got it. Normally when you update Firefox, then try to open a webpage in the "old version" that is currently running in memory, then you can't show the page; one MUST restart in order to use Firefox further. So this change maybe changes this "forced restart". This is probably more inline with the other programs in your system, that you can still use and need to restart in order to use the new version. Which makes totally sense. It's not what I thought, but it probably is.