Firefox crashes after upgrade to Flash 11.3 - How to fix!

Turns out that the latest version of Flash (11.3) will cause Firefox to crash on closing the browser after you've watched flash content, due to a new "feature" they added.

Here's how to fix it: http://forums.adobe.com/message/4468493
Note - they say the feature is for "Firefox 4.0 and greater", but it also causes the same crashing in FF 3.6.x! The same fix still applies though.