As of May 2010 with latest browser and operating system updates on Windows XP SP3.

FireFox
You should have no problems with any Firefox version after 2.0.

Internet Explorer
Widgets have not been tested and probably won't work in versions before 8.
Timers.html has a issue with excuting code prematurely that is kludged up with an alert box.

Chrome
Chrome Audio tag does not play wav files.  I drop back to play with embed
http://code.google.com/p/chromium/issues/detail?id=39713

Safari
Had no HTML or Javascript problems; but it did crash for no aparent reason while I was testing.

Other Browsers
Untested; however, if they say there like gecko, they will probably work fine.
My apoligies to Opera users.  Its a fine browser, but I never got around to making sure this stuff worked.

Firefox on Ubuntu
No problems.

iPhone
no embed support,  start at widgets page and select minimal UI, this removes some expalanatory text
and makes use on small screens easier

A lot of these pages were begun in 1995 and I have not made the effort to make them 2010 standards
compliant.

If you run these pages through an validator, you will find many errors.
Some are plain bit rot that you get when you edit html by hand over the course of 15 years.
Some are because this is DHTML and client side based Javascript
and the validators are not geared towards this type of content.

For example, my forms work fine; but the validators all complain that they are missing ACTION and other things.

I could easily make these pages snappier; but, I think their fast enough for my purposes.

Read the Timers help before you use them.

Clicking on the mailto has unpredictable results

We are blessed to be living in an age when we have a global communications network in which idiots, assholes, and total and complete wastes of $%^&* human life alike can come together to give instant feedback in an unfettered and unmonitored online environment -The Onion