In the continual struggle to be the best or most popular browser, the competitors do not always see it fit to be compatible. Here are two attributes that are used differently in each browser.
The table caption has not received fair treatment in regard to its placement by either browser. The default placement in both Navigator and Explorer is centered at the top of the table. In Netscape, align can be set to either top (the default) or bottom. There appears to be no way to get it flush right or left. In Internet Explorer, align was originally intended for horizontal placement. In version 2.0, the values could be left, right, or center. The valign attribute controlled top or bottom placement. In version 3.0, however, align is designated to do everything, taking the additional values top and bottom. Documentation for 3.0 does not list the valign attribute. You can still use it, though. It is not possible to set both a vertical and horizontal placement for the table caption with align only.
In both browsers, this attribute controls whether frames will have 3-D borders or simple rules around them. It is also usable in the <frame> tag. The trouble is that "on/off" values conflict. For Navigator, you use yes for 3-D and no for rules. In Internet Explorer, the value 1 means 3-D and 0 means rules. Go figure.