keep getting error message every time I open a browser

[ace3839]

an error message as follows keeps coming up when I open a browser:

TypeError:overlay[0] has no properties on line 149: on file: chrome//mypoints/content/xpcom/xuLEngine.js

have not idea what this means and have search all data bases that I can think of.
my system is fairly new, Windows Vista.
I am thinking that it may be a file somewhere that I have overlooked but cannot find it using the search on this new vista...(loved xp..vista is not what i expected).

[Broni]

I assume, it's Firefox, right?

Do you use "My Points":
http://www.mypoints.com/emp/u/index.vm ?
Did you install any Firefox extension fro the above site?