I've tried more than 5 different TTS addons, but none of them functioned as well as this one. Both English and Turkish is being read alout quite well and without any hussles. The initiation and ending of the reading is very intiuitive and works just fine.
I definitely suggest trying out this addon.

Intonation is unsophisticated. There is some kind of blowing noise, as if someone was speaking too close to a microphone, that is distracting and sometimes makes the speech unclear.

Good TTS Addon. But sadly i cant use Premium Voices because its not possible to LogIn, as it shows no Window or Field to do so. I use the same addon for chromium, but instead of the firefoxversion, its possible to login there. Hope this will get fixed in the Firefoxversion soon.

means absolutely nothing to me without the contextual menu that disappears after firefox closes.

5 star if they fix this issue. The shortcut Alt+p doesn't work the same way as the context menu and therefore can't be considered a replacement. The shortcut has to read the entirety of what was selected before you can make it read something else unlike the context menu button who interrupts the current text being read to start the new one you just selected.
The way I use this addon most of the time is to research subjects I'm unfamiliar with. I make it read while I keep looking at other stuff I'm researching. Most of the time, I understand what I was looking for mid read and I'm ready to TTS the next thing and it's already highlighted so I just right click to open the menu and make it read the next part I'm interested in which it does immediately by interrupting the previous text being read. The shortcut doesn't do that. If it's already reading something and I highlight something else and press alt+p, it just stops reading. If I press it again, it resumes the read of the previous text not the new highlighted one.
Could be solved by adding another shortcut like Alt+n (for next or new) to fix what's described above.

Another problem I have with this addon is that if you use more than one language, the voices options and choices become pretty much useless. In my case I want the addon to read both English and French texts sometimes. The only way to do this is to choose the Auto select option in the voice choices. Doing so give you a random voices for both languages and you have no say in what voice you want for each language. They seem to be chosen randomly as far as I can tell. The English male voice I got is one I hate and can't stand listening to, same for the french female voice I randomly got but that one is a little less annoying. If I select any other voice instead of the auto select option, then I'm stuck being only able to read one language because that same voice I chose butchers the other language it's not designed to read. I could go to the options and select the voice I want each time I switch between languages but who the hell would wanna do that?

glitches causing it to continue playing even after leaving sites, fast forward and rewind button don't work, highlight read text function doesn't work.

Esta muy buena la app, se lee rapido y con muchas opciones

This is a excellent add-on. I am Chinese and I can read English but I read very slow. With this add-on, I can read faster and can understand some of the words I do not know. The add-on also give us a lot of voice choices including man and woman voice.

This will get bumped to a 5 when you can tell us how to fix the context menu option from disappearing.

For the meantime, here are the short cut keys to do the same things:
To Play - Alt-P
To Stop - Alt-O
Go Forward - Alt-Period or "Alt-."
To Rewind - Alt-Comma or "Alt,"

If you should forget Alt-P - Click the button in the toolbar that looks like a megaphone, if it's playing, hit the stop button. Then click the gear button next to the play button. A larger "Options" box will open, at the top you will see "Edit shortcut keys" that will open a new tab with the short cut keys listed. Using Alt-P will speak what you highlighted. If you don't highlight anything, it reads the whole page I believe.

Oh and some might not know but the little gear button is also where you change the reading voice. I like the Amazon ones.

Hope this helps you folks out while we wait for the fix. Actually Alt-P might be easier to use than the context menu. If they made this option clearer, most people probably wouldn't care and again, I would bump my rating up to a 5, for the clarity.

One Ton Shadow ©

With the recent update it become completely useless.

The TTS (multi-language tts) worked well enough but stopped reading PDFs as FF was updated and the developer perhaps gave up. This add-on reads my PDFs beautifully and all the controls work perfectly. Thank you. Thank you.

Great usability. Amazon voice "Kimberly" sounds the best to me. Very listenable.

Yeah i like how it highlights. This Text to speech FF addon is awesome!!! Yay!

It does the job, however, the voice is one of those old-school 1980s movies robot voices. Still use it just wish the voice was a little different. Sometimes it's hard to understand the voice for technical Words which is the reason I got it but that's okay.

It works well but it gets stuck on things. For example if its italics then it reads it over and over. Same thin with numbers it will reread it over and over.

This is an awesome addon and is free/libre software