Happens in Firefox 3.5.
When you click on a link (almost any link I tried) on a page while it is still loading, you get a popup “cchost.js (5): SyntaxError: syntax error” or a red error message in the top with a similar message. This does not prevent the new page to load, though.
It may be hard to reproduce in a fast machine with a fast internet connection.

I’ve taken several runs at this one (it’s been happening for a while). I’m not done chasing it, clearly I’m doing something wrong, but nothing I’ve thrown at it (so far) seems to quiet the message.

The hard part about this bug is I’m never sure when it’s actually fixed (proving a negative, etc.)

Meanwhile, let me know if you’re still seeing it now…