Firefox has a built-in download manager. IE does not. IE downloads bits of information in sequential order, which tends to cause errors, especially with larger files. Firefox, and most download mangers in general, pick the bits of information up from all over, and then combine to make the file.I don't understand why IE would affect downloads. Whenever I download anything IE has nothing to do with it.
That's not a great explanation, but it gets the general point across.
As far as bit torrents go, you likely use a separate program for that, so no browser would have an effect on it.
There are some cool things with Opera...but some problems as well. It has some problems when you try to render certain types of web pages, and there are some applications that will not run in an Opera browser. That's why I prefer Firefox.I would test out both Firefox and Opera, I tryed out both for a while and ending up going with Opera, I just prefer the interface to fire.
Plus I don't use a ton of extentions, so I don't really have a need for for the fully customizable FireFox.
I also like the way the way that opera gives you a different tab instead of a mini window when you download things, you can do file converting if you have AVS (I think that's it) right in the screen where it shows you all the downloads, convert the files by right clicking on them
right in the download menu and convert them right there.
It really all comes down to personally prefence, try them both.