That's the relatively new "sandboxing" security feature. As noted in this blog --
-- there are actually three connected processes running: plugin-container.exe, which Firefox has used for some time, along with two instances of Flash Player. (In my task manager, for instance, "FlashPlayerPlugin_11_3_300_265.exe" is listed twice--each with a different memory "value.")
I don't pretend to understand the rest of it.
As for the sluggishness, there are a number of settings changes you can try for troubleshooting purposes to see if the performance is improved, such as disabling or enabling hardware acceleration for both your browser and Flash Player, disabling plugins, etc. If you're lucky, something might work to hold you over until all of this is fixed.
Same thing happening to me. I'm using FF 21.0 on Win 7. Two instances of Flash Player, each with different memory usage but browser crashes with Shockwave error very frequently. Have disabled hardware acceleration, no difference, still same Shockwave error and browser hangs.
FlashPlayerPlugin_11_7_700_202 is the version #. I've also gone the uninstall, reboot, reinstall route but again, no help.
Can someone please advise what might be the cause and a potential real fix? It's very aggravating. Thanks.