Let's begin with the eagerly awaited Firefox OS. Starting the debugger in Firefox OS has gotten way easier. There is a toggle in the settings app that will set or reset the devtools.debugger.remote-enabled pref, so that you don't have to mess with files and adb at all. At least for production builds that have marionette disabled by default. Developer builds will have to keep disabling marionette for a bit longer. You can find the Remote Debugging toggle in Settings -> Device Information -> More Information -> Developer. Note that you will have to reboot the device (or restart the b2g process) for the change to have effect. Also, as you can see in the screenshot, it's a good idea to disable out-of-process support while debugging, at least until the debugger can support it.
Speaking of desktop Firefox, the amazing Victor Porof has landed an obscene number of patches in the last few weeks, with many fixes and tweaks for the debugger frontend. Of those I'd like to highlight the new functionality to search for variables in the current scope chain while the debugger is paused. Prepend your search with a star to search in the variables view. When you deal with large objects with long scope chains, finding the variable you are looking for can be like searching for a needle in a haystack. Now it's a piece of cake.
|Searching for variables|
|Chrome debugging preferences|
|Browser Debugger menu item|
There has never been a better time to dive into Firefox internals and become a valued contributor. Take a look at this bug, to see how simple debugging has just become. Help us make the web better, by improving the lives of more than 400 million users!