Add firefox to the list of karma test browsers
Add firefox to the list of karma test browsers

tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs-core,tensorflow/tfjs-core,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs-core,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs-core,tensorflow/tfjs-core,tensorflow/tfjs-core