Sharing this Mozilla's recommended addons link. We normally don't install all from the list. Some of the favourites and very useful addons are :
PicLens,WOT,Downthemall,Clipmarks, Forecastfox,Download statusbar,PDF download,Shareaholic.
[ Recommended Add-ons ] [ Mozilla ] [ Download Firefox 3 ]
Google Labs has added lot of features in Gmail. Google labs says it giving these features for try out and these are not permanent,they might disappear sometime ! It gives you to lot of stuff such as photo in gmail browser chat, mouse gestures,Super stars, hide count, random signature, date format change,signature tweaks,pictures in chat and lot more.. . For some serious chat gurus.. there's a nice little thing saying "Email Addict" which makes you go invisible for around 15min and invisible too.(Shaanya can use this :P)
These are only some of the latest features added by Google on Gmail. There are lot more in the list. Just goto Settings>Labs in Gmail and enable whichever feature you need to experiment with.
How to disable these new features if something goes wrong ?
If by chance you enable some feature and it breaks or you are having trouble logging on to your account, just use this just go to http://mail.google.com/mail/?labs=0 and Labs will be temporarily disabled.