If you often use an Internet browser and email client together, you should give a try to SeaMonkey (Iceape in debian) that is a community effort to develop an all-in-one Internet application suite that stores both browser and mail settings in the same profile. It does use less computer resources than the combination of Firefox and Thunderbird running simultaneously. Here you have some add-ons I suggest for a complete gmail integration with Iceape:
- install gContactSync 0.3.5 add-on to have your gmail contacts offline;
- install Duck Duck Go for a search engine that does not collect or share personally identifiable information: it utilizes SSL to protect searches between the search engine and you;
- install Thread key 0.6 to group mails in threads;
- install ImportExportTools 2.2 emails in text or html mode (in Thunderbird/Icedove you can export emails and their attachments!).