Use of Google Web Speech API

I want to create a commercial web application based on speech recognition. I have found Google web speech api (http://ift.tt/X8uLyh, http://ift.tt/1B7uS1t) most suited for this.

So, can I use this api for free (libre, no fee) for my application and is there any limit on the usage per day?

Also, are there chances that this project will be closed and no longer available, though Firefox is also working on this API.