I also had this problem, on one of my sites, each time I open a pop up
window, immediately the error console popped up also.
I spent a lot of time looking for a solution for this problem, until
discovered that it was not a problem, it was my bug.
Pop up window was opened using a hyperlink, like this <a
href='javascript:' onclick='OpenPopUp();'>...</a>
Note the 'javascript:' part, that is the whole problem :-)
The link works in IE without side effect, but in Firefox, if you write
"javascript:" in the address bar and press Enter, it will open the
Error console, and that is normal :-)
I just fixed the above mentioned hyperlink to be like this:
<a href='javascript:void(0)' onclick='OpenPopUp();'>...</a>
And now it works fine! :-)
Not pretend that to be best practice, it is better than before ;-)
Hope that would be helpful to somebody :-)