If you want a on the fly translation I would say use Chrome as it can translate the site on the fly to your spoken language or to any other. This will save you time reading what it says and it does a pretty good job at translating. I use it for Japanese, Germany, French, Italian, Spanish, Dutch and it works very good. One might not like Chrome but in this respect it does a very good job at.

I don't think that the microphone on Google Translate has never worked with Firefox.

• https://www.google.com/search?sa=N&num=100&q=firefox%20microphone%20google%20translate