I have been using firefox for some time now - tab based browsing is a must for anyone who teaches on-line etc.
Firefox 2 has some great new features and extensions. The built in spell checker is great and works very well and has a british english dictionary.
Great extentions -
Zotero - collects references and webpages for research and can create bibliographies
Performancing - enables you to add blog entries to your blogs and automatically blog a webpage you are looking at - something I do often - has got me back into blogging
Cooliris - will open a preview page of any link - is already saving me lots of time as a surf the net, and use our VLE
find them at https://addons.mozilla.org/firefox/extensions/
See also - http://ukwebfocus.wordpress.com/2007/03/01/firefox-the-researchers-favourite-application/
which also has comments about institutional use fo Friefox in HE