Earlier this month, Adobe updated its Flash Player to version 11.3, but the upgrade has been a bit of a problem for Firefox users.
According to Mozilla's support page, Flash-based videos "may appear black, white or grey and never play" in Firefox since the update.
In a Tuesday blog post, Adobe acknowledged the problem and said it was "working closely with Mozilla to narrow down the issue and get it resolved as soon as possible."
One culprit might be compatibility issues between RealPlayer and Adobe Flash Player 11.3 in Firefox.
"Flash Player 11.3 introduces the Protected mode in Firefox 4.0 or later on Windows Vista and Windows 7. The Protected mode is a new security enhancement designed to limit the impact of attacks launched from malicious SWF files against Flash Player," Adobe said. "In the Protected mode, SWFs are rendered using a sandboxed Flash Player runtime. The RealPlayer extension for Firefox, Downloading & Recording, has compatibility issues with Flash Player 11.3."
Adobe published a workaround that "may solve the issue," it said.