I am having the exact issues:
Same day problem started, using newest flash version, also on iMac OS X 10.9.4 browser is safari. I've also uninstalled & reinstalled flash without resolve. Cannot have multiple tabs open when on broadcasting sites & youtube, as using the up/down volume both on keyboard & wireless headset produces "Plug-in Failure" message on all sites. Refreshing the page works, but cannot touch my volume without error message reappearing.
Would appreciate a solution promptly.
Nicole
