After opening a page, Firefox gave a warning that "Shockwave Flash is vulnerable and needs to be updated". I went to get.adobe.com and updated it to 17.0.0.169, but the warning was repeated and the content blocked. I checked youtube, which would play music and two test do-it-yourself tutorial videos without problem, but still repeated the block warning. I checked the Addons Manager, which indicated that Flash needed to be updated, but when I checked adobe it said I had the most recent update. Under Addons Manager for Flash, "always activate" grayed out, the option "ask to activate" selected but grayed when I clicked the drop-down button, and the option "never activate" the standard black text. After seeing a few other similar issues recently, I tried the "Forcing a Blocklist Ping" answer https://wiki.mozilla.org/Blocklisting/Testing#Forcing_a_Blocklist_Ping ...which returned "Undefined" in the Browser Console and did not have any affect on the issue.