Gmail Labs added two new experimental features: a "Mark as Read" button and a very basic script that warns if you write about attaching documents but you forget to actually attach them.
The attachment detector couldn't recognize patterns like "I attached a file", "Check the attached file", but it worked when using: "I've attached..." and "I have attached". Greasemonkey scripts like Gmail attachment reminder find their way in Gmail Labs and you no longer need to use Firefox or install a certain extension to use them.
{ Thanks, Carlos. }