Expand the logging utils and moving them to a new JS module
Let to change the chrome provider for locales

Experimental, enable it setting the preference:
extensions.simplels.provider

...to the name of any locale provider registered via chrome.manifest

It can be useful to developers testing the translation of their own
UI components in any locale supported by *their* extension.

Note that the "User Interface Language" window always will pick up
the list of available locales from the global provider, for to prevent
confusion from the text descriptions there, so it leaves, for the
moment, only to the toolbar button taking advantage of it.
Better internal descriptions for the language service

No changes to running code.
Drop the use of expresion closures

A non-standard SpiderMonkey extension, soon to be deprecated:
https://bugzilla.mozilla.org/show_bug.cgi?id=995610

Arrow functions can be handy in many of these cases, but not before
dropping the support of Gecko 23.