For one thing, <nobr> is not a W3C approved tag. It's something NS4 and IE4 both grok, but it's proprietary all the same. It's no skin off my nose that it doesn't work in browsers designed to be standards compliant, and it shouldn't be any off yours.
You should also be aware that IE 6 and Mozilla/Netscape 6+ have different rendering modes depending on the DOCTYPE line. If you're interested in having your pages look right, then you should always specify the doctype, although given that this ain't part of any X?HTML specification, that may not help.
If not P, what? Q maybe?