Firebug always showing JavaScript error "setting a property that has only a getter Line 0"?

Firebug always showing JavaScript error "setting a property that has only a getter Line 0"? I am on FF 3.6 on OS X with Firebug 1.5 and whenever I am using Firebug, no matter what website I am on, a Javascript error always shows up:
Asked by: Guest \| Views: 226

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Guest [Entry]

"Confirmed to have the same issue with FF 3.6.3 and latest Firebug, BUT even if I deactivate or even uninsttall Firebug the issue occurs.

Check http://www.pixenate.com and see if you get the same issue there. Most likely you do, so this is a coding issue with some web apps (like Pixenate)."