I never really noticed before, but Gmail uses Flash for uploading attachments. My wife noticed that she wasn’t able to upload multiple files at once when composing an email in Gmail. At first we though maybe it was the recent Firefox update, but then I remembered that she had just installed the Flashblock add-on for Firefox. This add-on is great for preventing Flash advertisements and other autoplay Flash movies. Usually you can still see where a Flash movie was blocked, but not in Gmail since the Google developers have done such a great job of gracefully degrading to a standard file upload control.

It’s easy to add sites to the Flashblock Whitelist, allowing Flash to load on those domains in the list. Just go to ‘Tools>Add-Ons’ then select Flashblock. Click on the ‘Preferences’ button, then ‘Whitelist’. Here you type the web site URL without adding the protocol, which for Gmail would be mail.google.com. Click ‘OK’ then close the Add-ons window. The Whitelist takes effect instantly, so you can start composing a new email right away and add multiple attachments to it.