Excellent browser that is more secure than IE. It does not (yet) attract hackers like IE does. Very many add-ons for fine tuning (see next link),
but these slow it down. But I still prefer Chromium.

All sorts of features to add to Firefox.

CHROME (Windows, Mac, Linux)
Alternative to Firefox and faster (from Google).

CHROMIUM (see specific OS links below)  (Windows, Mac, Linux)
The underlying app for Google Chrome. Its advantage over Chrome is supposedly that it has no tracking of your "browsing history" by Google, 
 but the Chromium download has a Google URL.
Windows and OS-X Versions                               Ubuntu & Mint Versions

From Apple. I have had no need to try this out, but presumably it allows Apple to track your browsing a la Google.

OPERA (Windows, Mac, Linux)
Strongly recommended. Opera originated browser tabs, and now includes an email client. Perhaps the most secure browser of all from what I have
read (combined with Linux possibly the best). I use it only for important web uses