"Facebook is adding additional iframes for security reasons and they did not realize that user agents' default styles sheets in some browsers contain rules such as iframe{border:2px inset; } , they will probably fix this soon, but this is a problem on facebook's behalf meanwhile you can fix this issue by ......"
I'll see if I can get the code in the right place sometime today.
What that actually says is Facebook changed something that is mucking up the default settings in your browser.
The forum just happens to use a component that triggers the issue. It always has. It's the short sighted move on FB's part that is causing it to show up now.