In IE6, setting clear to both in a span tag seems to work, whereas it
doesn't seem to work in Firefox.  A demonstration can be found here:

http://www.frostjedi.com/terra/dev/test3.html

Any ideas as to why this might be, and what can be done to make
Firefox's rendition of the page the same as IE6's, without using div?

Also, I tried replacing nested css stuff (ie. #div3 p, #div3 span) with
their own id's (ie. #p and #span) and am now getting different
renditions.

Here's the orig page:
http://www.mezzoblue.com/tests/centered-css/ex4.html

Here's the modified page:
http://www.frostjedi.com/terra/dev/test.html
Any ideas as to why there's a difference in rendering?  Thanks!