Firefox is a great web browser, there is absolutely no argument about that. However those of us who are using linux long enough have went by quite well without it, and some still do. In the spirit of linux and open source (not so much for opera), it is only fair that we are aware of alternate options for linux browsers out there. Here is an attempt to list some of the linux browsers actively developed and updated.
This list is not comprehensive, most of these browsers are not exclusive to linux OS; and because most modern browsers use gecko engine and evolved from mozilla/netscape some of them have familiar layouts. If I missed out any popular browser do let me know in your comments.