Despite reports that Firefox 1.1 would appeal to corporate users it will never actually surface. It is taking the developers longer than expected to implement new features, so they release date has slipped back. However, as a result they have said they will include even more features into the next version of Firefox. Given the extra features, the Mozilla team has decided to give the release the grandeur of being called Firefox 1.5.
Expect to see a beta version released next month, with a final release in September, although be forewarned that the Mozilla team don't like to tie themselves down to specific release dates.