This is a known bug in Mozilla.

There is a bug in the jsd (the debugging module of the Mozilla engine) dealing with code defined by an eval statement. If the code run by the eval is brought up in the debugger, it is reported as the line of code which executed the eval itself, plus the line offset within the eval. Since Dojo uses xhr + eval to load all code outside of the bootstrap, this is what you will typically see throughout your callstack when attempting to debug Dojo code in Mozilla.

IE and Safari debuggers correctly report the eval buffers when debugging, though the actual location corresponding to those eval buffers is not available to the debugger.

Pending a solution to this problem, you can try an experimental patch to the Firebug debugger which solves this problem.

Two other workarounds include manually inserting tags to load each module of source you wish to debug, explicitly loading it prior to the Dojo bootstrap, or using the debugAtAllCosts option.