Update: Venkman is probably no longer the solution to any problems that anyone still has.
- For historical information see Venkman on MDN
- To get actual debugging done, see the built-in Firefox developer tools or Firebug
Thehas the advantage that I've done the install wizardry to make Venkman installable directly without needing to download it first.
There is a known bug where you can't launch Venkman twice in a browser session. I think this is because the close button on Venkman just hides the window rather than releasing all the resources.
If you want to install, you know where to go.