Comment 10 for bug 274468

In response to John Vivirito's comment #9 - obviously the prompt to close *BEFORE* executing the update would have minimal impact on multitasking.
Imagine you have 9 updates, and firefox is, say, 7th of 9.
The prompt would only trigger on launch of the 7th update, the firefox one, in a similar fashion to click through license agreements for proprietary software. At that point you would indeed have to halt your "multitasking"
But in the current layout you have to do that anyway only seconds later as soon as that unpack of #7 is complete - if you don't, Firefox starts behaving unpredictably.

In short, this doesn't really improve the user experience at all, and has clear negative impacts in confusing users, and even causing profiles to fail.

Both of these make for a worse experience in Firefox updates under Ubuntu, than when Firefox updates are handled by Firefox (say under OSX or Windows or just the user launching their own Firefox)