Here at DW Alliance we use Firefox as our primary browser followed by Internet Explorer, Safari and Konquorer.
Our favorite Firefox features are tabbed browsing, scroll wheel clicking on a link and drag a tab.
The fastest way to open a new tab is to use your keyboard buttons 'ctrl+t' for windows and linux or 'apple+t' on a mac. Depending on your browsers configuration it will will open a new tab in the existing window.
Scroll wheel clicking on a link will open that link in a new tab.
To keep your tabs organized you can drag them around.
One other nice but less used feature we like is to open a folder of bookmarks all at once. We use that feature to monitor our various servers spread across the planet running ntop.