Looks bad - and highly visible. Should probably block.
A screenshot would help.
likely bug 494657 which replaced 16x16 icons with 24x24 icons. verifying this before I mark dependencies.
Looks like this has been around for a couple months (http://dougt.files.wordpress.com/2009/04/200904301321.jpg, f.e.) it just became more apparent when the icons were changed in bug 494834.
I'll take a look at this.
Created attachment 381114 [details] notification x now looks complete Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.2a1pre) Gecko/20090602 Minefield/3.6a1pre Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.1pre) Gecko/20090602 Shiretoko/3.5pre