I use Firefox as my primary browser because it helps when learning tricks other website is using (with DOM inspector and JSView plugin).
I use IE only when running WindowsUpdate and debugging my ASP.NET application.
Honestly speaking I don't know why the number of useful plugin in Firefox would out-numbered IE that much. (In IE, all the BHOs are arguably falling in one or two types only - toolbar for adblocking and searching, then downloaders) Most developers should have
been more familiar for IE right? But seems most who do have skills on developing IE pluggins are most interested in kidnapping IE preferences...
There are tons of IE plugins, but they're not all that widespread or talked about much.