Check for update

• Remove and install "web sling player" plugins

There doesn't appear to be a way to "Remove" plugins, only disable them. In any case I installed an older version, then reinstalled the latest version but no luck. Web sling player works with Safari on the same computer but not with Firefox.

Are you in safemode?

No. It used to work fine, but I think either the latest Firefox or sling player update broke something.

did you check if you firefox is in 32 bit mode ?

http://www.simplehelp.net/2009/09/15/how-to-run-os-x-programs-in-32-bit-mode/

Sling players work only in 64 bit mode for osx