Privacy is the thing we should care. But trade-off between privacy and convenience prevents many people from signing and encrypting their email. I'm also one of these "lazy" people.

Problem arose when my friend sent encrypted message to my gmail inbox. I can decrypt it easily with Thunderbird and Enigmail, its brilliant extension but I don't want to bother using full-feature email client for only one message (I haven't used POP3/IMAP for a while). I need to find another solution.

My savior is FireGPG, a Firefox extension that automatically reads my private key from my home directory and provides sign-encrypt-decrypt functions. Once the next encrypted message come up to my inbox, just highlight the text, right click and select "decrypt", that's all.

FireGPG web site said that it works on Windows and Linux (you still need to provide GPG application manually) but it should work on Macintosh.

Only disadvantage of FireGPG is the decrypted text will show up in new window. I know that it can't be done technically via extension. Anyway, it's possible if using GreaseMonkey and Gmail Encryption script.