If you look at http://www.mozilla.org/releases/ you'll see: End-users are encouraged to use our latest stable[1] build. [1] http://www.mozilla.org/releases/stable.html That page will tell you Mozilla 1.4.1 (not 1.5) is appropriate today. Here's a nice diagram illustrating the different branches: http://www.mozilla.org/roadmap.html -=EPS=-