Many people (including me) have switched to Firefox or Mozilla by The Mozilla Organization. Unfortunately, every browser will interpret HTML a bit differently (like how it interprets slightly bad coding). If you're maintaining web pages for your digital library or digitization project, please check to see how the pages look in Firefox or Mozilla. Do the pages look as you expect? Do the menus work correctly? Don't assume "yes."
One site that I visit daily works better in Internet Explorer than Firefox. Right now, firing up IE is a just a nuisance, but soon it'll be a royal pain and I'll stop using that site. Don't tempt your users to stop using your site just because yours doesn't work with their browser.