Jeg fandt dette nyttige svar i et andet forum:
I tried with several FP versions. Flash movies worked on IE but not on FF, and I got report "You need to install FPlayer 10.1 or newer version". This simple test site told me Flash was not installed on FF and was installed on IE.
http://isflashinstalled.com/ I did several complete un-install and install operations. I even used the Uninstall tool on Adobe site.
Finally I tried this "FlashDisable 0.9.4" FireFox add-on.
https://addons.mozilla.org/en-US/firefox/addon/flashdisable/?src=api This add-on is intended to allow user to turn Flash Player on and off, when needed.
After installing this, I clicked Flash Player ON, restartef Firefox. Finally Flash Player started to work as it should. Also the test site above now reported FP is installed.
... Brug det første link til at checke, om Flash er intalleret korrekt ved at tilgå linket i Firefox. Brug dernæst det andet link til at tænde/slukke for Flash i Firefox.
Hvis ikke det virker, foreslår jeg stadig, at du afinstallerer Flash helt og dernæst installerer det på ny ved at tilgå
https://get.adobe.com/flashplayer/ i Firefox.