The important thing to remember when designing pages is to view your page using different browsers. They will handle many parts of HTML differently, especially Java.
The two big players in the browser war are the following:
See Browsers Castro p. 20 (alt. p. 14)
Many people are not aware that other browsers are available like Opera which is a good choice for people that have older computers because it is fast and small.
Practice viewing these pages in both browsers and notice the differences between how Netscape and Explorer display WebPages.
How will you make arrangements for viewing your pages in both browsers.
HTML Versions
There is a more systematic way to approach the problem. There are many resources that compare the features supported by various browsers with their own extensions as well as sequential versions of HTML.
The first definitive version was HTML 2.0 -- this had most of the elements we know and love, but was missing some of the Netscape/Microsoft extensions, and did not support tables, or ALIGN attributes.
HTML 3.2 was the next official version, integrating support for TABLES, image, heading and other elements, ALIGN attributes, and a few other finicky details. HTML 3.2 is the current "universal" dialect -- essentially all browsers understand HTML 3.2. IT was, however, missing some of the Netscape/Microsoft extensions, such as FRAMEs, EMBED and APPLET.
HTML 4.0 is the current official standard. It includes support for most of the proprietary extensions, plus support for extra features (Internationalized documents, support for Cascading Style Sheets, extra TABLE, FORM, and JavaScript enhancements), that are not universally supported.
Here is a really good reference on Netscape/Microsoft Extensions to HTML:
http://www.utoronto.ca/webdocs/HTMLdocs/NewHTML/netscape.html
See HTML and Compatibility Castro Appendix D pp. 315-321 (alt. pp. 361-368)