Those who still "have" to use IE because of Windows Update, there's hope for you:

Windows Update extension for Firefox (and more)

Note: I do not know if or how this works, I do not have Windows at all.

Here what it does and does not do.

What it does not do, is let you use Windows Update via Firefox

What it does do, is open an IE window which is taken directly to the Windows Update site. But you still have to use IE.

I think for Firefox to properly use Windows Update (which may never happen) is that it needs to fully support Active X. I have yet to see a good active x plugin yet.

Firefox would also have to trick the Windows Update site into believing it is IE.

And lastly, I imagine Mr. Gates has slapped more than a few lines of code embedded deep within IE to ensure it is the sole source of Windows Updates.