Very Robotic Voice for a 2014 Year! Rated 2 out of 5 stars
The voice is very robotic and not clean. Come on now. We are in 2014. Text-to-speech voices have become more human-like.
For now, the best "Firefox addon" is the "Im Translator TTS". They have a male and a female voices which they have very natural voices and speech. I Suggest you all to take a look at Amazing Services offering tts Voices, very WOW and realistic sound. These Services are IVONA, Loquendo, Nuance, Acapela, Neospeech, Cerepro, and You will never want to listen to any robotic voice again. I hope you include the Greek Language in your future development. :-)