There actually isn't any source! The application is made with Fluid App and I've tweaked the defaults.plist inside the application to reflect our specific requirements, so if you want to change the way it works you just need to play around with the various settings inside the app itself. If you find anything particularly useful then post your ~/Library/Preferences/com.fluidapp.FluidInstance.mbed.plist and I can work your settings into the defaults.
Unfortunately because it was made using Fluid I can't change some of its behaviours (for example I can't overwrite previously downloaded files).
If you have a different drive name you can alter the default download directory in the 'General' section of the preferences.
Thanks for your quick response - I'm glad you like it!
Its only a dedicated browser, but it means your compiling can have its own window, and I can add little tweaks (like having your compiled code downloaded directly to your mbed).
Download it here and let me know of any suggestions for improving it!