Seeing a lot reports about Windows error messages when clicking a bookmark or link in email. I think this is generated by link handling if you're switching the default browser away from IE to Firefox 0.9. It isn't (or rather, wasn't) an issue with previous Firefox builds. I checked the MSDN site and they say the fix is to switch back to IE6 – which does work – but it doesn't seem like much of a solution.
If you're getting error messages when launching Firefox 0.9 from a bookmark or link, you probably need to disable DDE for that registered file type.
To disable DDE, access My Computer and select Tools > Folder Options > File Types. Select the registered file types that show (NONE) for their extention and seem to be web related.
Start with Internet Shortcut. Highlight it and select Advanced. In the advanced config, highlight Open and select Edit. Remove the checkmark next to Use DDE.
Repeat this for other extentions as needed, perhaps URL:HyperText Transfer Protocol and URL:HyperText Transfer Protocol with Privacy, at a minimum. You may want to come back for the FTP, Mailto, etc if you continue to get error messages.