You get a bunch of errors when you write Javascript that tell you that the error is on some line in your code. Unfortunately Mozilla doesn't tell you what line you are on, and doesn't even have a goto line function so that you can find out what code has the error.

Bug 15364 -- Add line numbers to View Source Bug 79612 -- [RFE] Source file links in JS Console should jump to line number of problem Bug 104383 -- Ability to go to specific line number in View Source window I've moved the first and third of these into the viewsource component so they're actually findable. :) *** This bug has been marked as a duplicate of 15364 ***

vrfy dupe