Enter FireBug. It's not entirely intuitive, but at least it gives some pointers and displays the error messages that would otherwise fail to be displayed. At first, I thought FireBug would just start spitting out the error messages, but I needed to configure it first. Again, it wasn't much, but it did take me an hour of searching the web to just give up and try poking around. The "Console" button was what I wanted. Displayed nice error messages so that I could track down the bugs. (Not that they're all fixed yet, but at least I have a direction to look!)
Very valuable! Thanks so much.