Same here. Crazy to think that I've been using it for over 15 years and never had a reason to change. I've tried other browsers, but none of them gave me a compelling reason to continue with them.

I think the most probable reason for that has been the complete support for addons that no other browser ever did. For instance, why doesn't Chrome have support for vertical/tree-style tabs without using a separate window? That one feature alone keeps me on firefox. By removing the tab bar at the top of the screen, you regain a significant amount of vertical space on a laptop.