About the only diff I see in firefox is that you can't do things as far as security, (activex is disabled by default, and there is no chance of changing that) certian things like banking and such are not available to use. So you will need to use IE for that. Other than that Firefox is a very good browser to use.
Well I almost forgot - Since ActiveX is not in the program media playablity is also not very good. Reszing of media windows is not available. The only functions are the minimul. Some of the plugins for media content don't work. There are some pages that you go that will not allow you to view because of using firefox.
I know I based it all on activex, well my opinion is they should have a a smart activex system. Otherwards, Say you go to a site that requires it. A pop up comes up saying that there is activex and proceeds to ask you if you want to enable it for that site or not. If you say yes it adds the site to a safe list, if you say no it adds the site a block list. This way certian things will be able to work right. I feel the biggest problem firefox is having with certian sites is because activex is nto available. I know there is an extension you can download, but that does not work very well ...
Anyway, end of rant ..