Haven't been able to get it working on any website...
Will try a bit more and update if even one works, but as of now... I highly recommend you avoid this extension.

All I can say is that it's better than the MS-Windows Narrator. :(
It doesn't work on all websites, nor my web-based email; & ...
It needs options for changing the voice & the speed that it reads.

An option should exist to adjust the speed of the voice