Originally was a Firefox user way back when it was first released, but ever since discovering Opera in 2005 it has been my main browser
.
I have every browser installed on both OSX and Windows: Chrome, Firefox, Safari, and Opera. At times I may use another browser for this or that yet Opera has stayed my favourite as it's customizable to my taste in every way: from menu items, buttons, shortcuts, userscripts, the list goes on, and all without any additional addons.
Other features I love: the easy tab management is superb (
tab stacking ftw), the ability to create custom search engines from any search box, the in-built RSS feed reader, the closed tabs menu, and the
single-key shortcuts (1/2 to navigate tabs, z/x for Back/Forward).