Gecko:ErrorMessages

DOM Scripting Error Messages

DOM scripting error messages are currently really bad for Web developers. Much of the time when something goes wrong during script execution, there's no feedback other than a JS exception with pretty much no information about what went wrong. Debugging the error is an exercise in guesswork and testing. We could do much better; many of our codepaths that just return NS_ERROR_FAILURE actually know at that point what the real error is.

Adding better error messages doesn't seem like a very hard problem, it's just a considerable amount of drudge work (and perhaps, has to be done carefully to avoid bloat).