This fixes the dictionary manager and various other places where a XUL
element was being created with createElement(), and also simplifies a lot
of createElementNS(HTML_NS, ...) calls.
This might cause some minor regressions but everything tested has
worked. Not touching preferences (#2659) or bindings.
- The Mozilla CommonJS loader is no longer available, so bundle the
Fx52 version of it
- Strict mode is enforced
- `this` is only defined as a global object in .jsm files, not .js files
- `this` can't be converted to a string for BackstagePass test, so check
for presence of Components.utils.import instead
- The return value from import() is no longer available
