We have some bugs on file already about automatic pretty-printing not playing nice with chrome debugging (bad heuristics), but they expose another bug: stepping on a pretty-printed (source-mapped) file will pause in source map library frames out of nowhere. STR: !) Open the debugger on a bugzilla page. 3) Open the browser debugger and select debugger-controller.js 4) Set a breakpoint at line 296 (onTabNavigated). 5) Reload the bugzilla page. 6) Step in for a bit and you will get to pause on SourceMap.jsm:410 This seems like the same problem we faced with the promise library back in the day, which was fixed by loading the library using loadSubscript instead of Cu.import.

If Panos is right, the proper fix for this would be to convert SourceMap.jsm to an SDK module. The devtools loader will automatically mark modules as invisible to the debugger. Bug 935366 might be relevant for this.

I think this should technically belong to the source maps meta bug, since the problem is presumably with SourceMap.jsm.

This is going to be fixed by bug 935366, which drop the jsm in favor of a regular commonjs module.

SourceMap.jsm is gone now.