Recently I have been surfing around using
Mozilla and I am amazed at how many web sites are not coded correctly for it.
I know it ain't the browser of choice for most of the planet, but it does show up some errors in coding which are forgiven by IE.
I saw a webmaster site yesterday which was image sliced and looked fine in IE. But with Mozilla there's two big gaping horizontal gaps.
Of course I have not emailed the site owner because I don't give that much of a s**t.