You've got some sort of developer oriented extension installed, and it's reporting errors in scripts on pages.
It might help if you list off the installed extensions on your system. Everything listed under Tools-->Extensions
I have been using Firefox for over a year now and I love it. Well, used to love it. I still use it, but I get annoying error messages all the time now that I don't know how to get rid of. Whenever I click on a link to open a new window, I get this message: ''! TypeError: this. docShell has no properties''. My only option is to click ''OK'', then the new window will open and then I get that message again. I click OK and then usually it is fine (until I try to open another window). Twice I uninstalled and reinstalled Firefox and the same thing happens. It didn't always do this, and I think it started when I moved in January, or shortly thereafter. I have searched the internet and couldn't even get a hit on a similar problem. I am running Windows XP SP2 and Firefox version 184.108.40.206, Avast antivirus, Spybot Search and Destroy, and Ad-aware, and I cannot remember installing anything new right before I started getting these errors. I would appreciate any suggestions you may have, because I really want my error-free Firefox back!