Download Zotero and choose from the associated plug-ins using these links:
Zotero works on all three major operating systems: PC, Mac, and Linux. It works best with the Firefox browser, but you can download and install plug-ins for the Chrome and Safari browsers as well.
Zotero Quick Start Guide - from the folks at Zotero
Once you get Zotero installed on your Firefox browser, look for the Zotero icon on the lower right side of the browser.