Firefox does not do email, but there are enough users here that someone might be able to help you anyway, if you indicated what web based email you are using and how you are attempting to add the attachment. And when it stopped working, if you can improve on that statement. What is the file extension of the attachment. Looks like you provided the exact wording on the message so Googling that including the enclosing quotes. Seems to show the number 1 answer comes from Yahoo answers -- so for maybe they have the biggest problem the example will assume it is yahoo, though they all have these same two problems. Such problems often occur more frequently when the website makes major changes or when Firefox comes out with an updated version. I think Yahoo changed their site they wanted me to update to the new whatever. Clear your cookies and your cache * clear your cookies should be clear your Yahoo cookies. *# Tools > Options > Privacy *# search on yahoo *# try clearing the mail.yahoo.com cookies, if that doesn't work try extending the range within yahoo's cookies. * clear your cache, Tools > Options > Advanced > Network > "Clear Now". :To prevent problems in the future, suggest clearing cache upon exiting Firefox :see http://img232.imageshack.us/img232/4928/clearcachew.png Yahoo provides good picture documentation on their site and better and safer than Mozilla's support example for Firefox (which requires you to read carefully or end up destroying all of your history), but I think my picture above is better as it shows both panels side by side. But you might want to the the same for other browsers from their documentation as well.