I'm currently in the process of setting up a new development machine with all the software I need (Oh what fun!)
I was working may way through my list of essentials (about 90 items and counting!) - installing from disk for stuff on disk, and downloading the most recent versions of apps available on line.
Shortly after installing MS-Office (and running MS Update and rebooting), I tried to download iTunes... I.E. crashed as soon as I had clicked the save to disk button. I tried again... I.E. crashed again. So I thought - lets download FireFox and use that instead... I.E. crashed again.
Thankfully I had a somewhat recent version of FireFox on an external hard drive - and I was able to install that and download without any further issues.
If I hadn't had FireFox - I would have been left in a position where I couldn't really do anything - not being able to download anything would prevent me from downloading a browser which is capable of downloading software...
I've had a worse problem than this in the past - with Internet Explorer refusing to load at all on a live web server, as it had been updated and the machine had not been rebooted - rather an issue when most of the monitoring and configuration tools on the server are browser hosted...
Needless to say, I keep a copy of FireFox on all the servers now!
Rant over for now :)