Mozilla's Firefox has become known for it's feature set and lack of exploits(well, compared to IE), and it can be argued that it's the better browser to use at home. In a corporate environment however, Internet Explorer's integration with Windows and other factors can outshine the usefulness of Firefox.
"Two years ago I blogged about a similar subject. I discussed the advantages of Internet Explorer (IE) over Mozilla and other web browsers in a corporate environment. I concluded that IE is by far the better choice. Recently we deployed about 250 new computers and so I considered this question again. Now, Firefox is the main rival of IE. The decision was not so easy this time, but IE won again in the end."