Add Pale Moon compatibility

This PR will add compatibility of FireFTP with Pale Moon 25.0+
Since Pale Moon uses the pre-FF32 API that was switched away from in FireFTP 2.0.21, I had to split the code paths, restoring the previous state for Pale Moon in its own XUL/js modules.

I've tested the result on both Pale Moon 25.0.1 and FF33.0, and both seem to be happy with this.