The source code is here: http://mxr.mozilla.org/services-central/source/fx-home/ What should I be looking/search for? Or even how to extract /ffhomeDB.sq3 and see what it contains.
Look for uses of the file protection API, for example the file protection classes and constants.
If it uses keychains it should also be using the keychain protection options.
Generally speaking you'd expect telltale constants and methods such as the following (not exhaustive) to appear in the code if it is aware of the new data protection APIs:
NSDataWritingFileProtectionNone NSFileProtectionKey NSFileProtectionComplete NSFileProtectionNone
And it should be responding to lock / unlock events, i.e. should implement: