Bewertet mit 5 von 5 Sternen

make sure flashdisable is not enabled before you uninstall this add-on, otherwise flash will be disabled every time firefox starts.

Diese Bewertung wurde für eine vorherige Version des Add-ons ( abgegeben. 

This is a problem with the Addon Manager. I uploaded a new version which uses an other API that should fix the problem:
You may have to restart firefox several times (5 in my case) and each time enable Shockwave Flash using the Addon Manager to finally re-enable it.