While not doing an annoying quote-by-quote rebuttal of some of the comments, I'll make a few points.
- It is absolutely stupid and foolish to tell your users to use one browser, and moreso to force them to use one.
- Write standards-compliant code without browser-specific code and your site will look perfect in browsers by Mozilla and usually good in IE.
- Firefox strictly follows W3C standards, so if your page looks bad in Firefox, it's usually your own fault.