I'm able to consistently reak firefox. I'm unsure if this is a Flash problem or a Firefox problem. But, these are the steps:
Go to the real arcade Daily Jigsaw Puzzle, here: http://www.realarcade.com/onlineGamesProd?gameid=superjigsawpuzzle&src=ogpg&tps=ambient_
Click the play now button. Play the game. ( My top time is 3:01, although usually I'm in the 3:30-4:00 range).
After finishing the game, close the game window, then close the real arcade main page.
As an aside complaint about RealArcade, the game window is too long and stretches off my 1280 x 800 screen. Does the common user of RealArcade really use a higher screen resolution? I doubt it.
Anyway, after you close all active firefox windows, try to reload firefox. It won't let you, saying that Firefox is already running.
Here is the fix:
Basically, you have to shut down the process manually before restarting Firefox.