Diesbezühlich kann man dir im Mozilla Support helfen.
[Link:
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Ich hab im Internet eine Lösung gefunden vllt. klappt sie ja bei dir. Die Anleitung ist auf englisch, ich poste die Anleitung mal hier.
"WORKS with Flash 12, if added to trusted location with EXACTLY this path:
jar:file:\\\C:\Users\<Your profile Name>\AppData\Roaming\Mozilla\Firefox\Profiles\<Your profile folder>\extensions\{ef4e370e-d9f0-4e00-b93e-a4f274cfdd5a}.xpi!\chrome\content\foxTab_flash10.swf?v1_4_1
You must add exact location of swf file (located in xpi/jar). See example above.
REPLACE <Your profile Name> and <Your profile folder> with REAL ones on your PC.
Attention! If you have non-ASCII letters in you profile folder, you must replace them with URL-encoded version (except spaces).
Use [Link:
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Go to: Control Panel -> Flash Player -> Advanced Tab -> (scroll down to see) -> Trusted Location Settings -> Add
to add Your EXACT location"