Add support for TTS to work in Firefox and Brave browser.

**Description**
Many users use the book-reader TTS feature for listening to audiobooks. But readers who use browsers like firefox and brave are not able to take benifit from this feature.
**Evidence / Screenshot (if possible)**
When we click on read out loud button on firefox web browser it just highlights the text without speaking out any audio.
typing ``speechSynthesis.getVoices()`` returns an empty array in the console.
**Note: I have just tested this on Ubuntu operating system the results can vary with different OS**
**Expectation**
TTS should read out the text.
**Tested On**
Ubuntu 19.10
Mozilla Firefox for Ubuntu canonical 1.0
Browser version 74.0 (64-bit)
**Proposal & Constraints**
speechSynthesis varies with respect to browser thus there is a need for writing separate code to handle other browser support.

**Stakeholders**

> @-tag any stakeholders of this bug