The Firefox Extension has only two Microsoft electronic voices. The explanation for the app provides a list of other voices that are available but does not provide any explanation about how to add those voices.
Because of vision problems, I need text to voice and I am used to just playing the highlighted text without having to copy and paste it. I do like the play, pause, resume and stop buttons - those could be just the universal symbols for those commands. It is annoying to have to delete the text once it has been spoken - it seem like that should be automatic.