Add FeatureDetection.isFirefox and firefoxVersion.
Add basic tests for FeatureDetection functions.

Also clean up logic in the methods a bit, and fix JSHint.
Merge pull request #2207 from AnalyticalGraphicsInc/detectFirefox

Add isFirefox and firefoxVersion to FeatureDetection
Merge branch 'master' into compressNormals
Re-add compressing normals to a single float.
Add doc and error checking.