An interesting article came up on CNET Download.com about a Firefox extension I wish I found long ago.
Its User Agent Switcher which lets you pretend to be another browser. Opera has something similar to this built in. Handy for those sites that simply won’t load in Firefox. Unlike IE Tab (and related add-ons) the site still uses Firefox, only pretending to be other browsers like IE by “switching” the user agent.
Be aware however, that many sites want Internet Explorer because their site breaks in other browsers.