Flash: Video File not found – just in FireFox

Dear colleagues and folks, I’m just experiencing a problem with flow player right now. I had it running yesterday with a software encoding solution, and this worked fine for a HLS live feed. It did not matter if the page was viewed inside Firefox, Safari or on a iPhone; all three devices played back the video as expected. Now, today – same setup: Safari plays the live stream quite fine, Firefox tells “Flash: Video file not found”.
Can you help me ?
I’m about to buy a license for this plugin to use it as it’s a good tool, but I’d need to understand why the same page now behaves differently than yesterday.