Rather than directly accessing the JavaScript engine this seeks to use
XPConnect to communicate with JavaScript. The idea was actually based on
an earlier version of SWT but the relevant component was never used.

* Revert to using the previous mozilla / profile paths for XUL < 24
* Remove with() from evalAsChrome as alters security context

Change-Id: I63a2b085a96193904c0d67d960e158233464ca56
Signed-off-by: mjgp2 <matthew.painter@import.io>