There are some compatibility issues between the latest Flash player and some Firefox add-ons or settings. Could you see whether anything in this article helps: Flash 11.3 doesn't load video in Firefox.

jscher: Thanks for your help. It probably is an issue with Flash 11.3, as I see in my installed Plug-ins (accessed via Tools/Add-ons) that Flash was just updated yesterday. (That must have happened automatically, as I wasn't notified of it or asked to approve the update.). But, if I downgrade to Flash 10.3 or 11.2, as suggested in the article link you provided, won't Flash subsequently automatically update again to the new, apparently problematic 11.3.300.262 version?

See: Flash Global Notifications Settings Panel

• http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager05.html

Thanks to you both for your help. I uninstalled Flash 11.3.300.262 and downgraded to 10.3, and all functionality seems to be restored.

A couple of follow-up questions: Do you know if Adobe is aware of the problems with the most recent 11.3 upgrade? If they are, is it likely they will be issuing another upgraded version to correct the problems? And, would it be advisable to install such an upgrade, or am I better off just staying with version 10.3?

Thanks!

Flash 10.3 is being updated in parallel with Flash 11.3, but I'm not sure for how long. Flash 10.3 is safe for now.

Flash 11.3 has a new protected mode for Windows Vista and Windows 7 which should offer enhanced security for users, but you might give it another point release or two for the incompatibilities to be resolved.