Today I install 2 more add-ons, both are to improve my GMail accounts.
1. Better Gmail 2. This utility modify a little (pimp probably) the normal view and use of Gmail, attachments are symbolic images describing the content, colorize the pointed message and more options are available. An excellent job of Gina Trapani from LifeHacker.com https://addons.mozilla.org/en-US/firefox/addon/6076
2. Gmail S/MIME. Talking about privacy, this add-on allow us to sign and crypt messages, a must-have for every-one, you cannot know who's watching in the upper cloud. https://addons.mozilla.org/en-US/firefox/addon/592