To my astonishment, the majority of the netWindows core scripts function without problem on Konqueror 2.99. That's a long way from having widgets and a content loading system that work on that browser, but it's a couple hundred percent more than I expected to be functional. Guess it's proof that if you code defensively and work with the standards your code will be viable in places you couldn't envision it. And those are types of applications that tend to really matter, the ones we don't think about.
Today I also discovered that in the JS debugger (Venkman) build included in Mozilla 0.9.9, there is a profiling option. The profiling information it kicks out is super useful for understanding what takes how long and why. I can tell already that it's going to be absolutely invaluable in tweaking 0.3.0.