Firefox doesn't have a built-in emailer, so I'm guessing you are using your provider's webmail site. Each site has different buttons for adding attachments. Do you want to indicate which one you're using to see whether anyone can provide specific comments?

Also, your browser reported to the forum that you are running Forefox 3.6.13, which is a very old version with numerous publicly disclosed security vulnerabilities. Is that version number correct? (You can compare Help > About Firefox)

Tks I am using both gmail and mac for sending messages. I will also update to latest firefox per your info.