Double-Click Protection in Firefox

A common class of errors in web applications is failing to handle the same request twice, as occurs when a user impatiently clicks a link or a button a second time while the first request is taking longer than usual.

Recently, someone reported an issue just like that on an application we develop: If you click an image button twice, the system gets, shall we say, cranky. This morning, I attempted to verify it using Firefox 2.0.X, and couldn't do it.

I tried the same thing in Internet Explorer 7.X, and voila. No problem, error verified.

That seems to imply that Firefox (or possibly one of the extensions I use) is protecting me from a multiple-submit problem. Interesting. I wasn't able to turn up anything in a quick Google search; does anyone know more about this?