Used this for like years to make my novels audiobooks and the desktop browser version of it works pretty well. IMO, the only good TTS voice is the microsoft zira one lol. Works very well for what it is, but the in-built firefox reader also has a TTS function, which is essentially the same thing. I don't discourage people from using this extension though, since it comes in handy when you just need one specific section TTS'd and it's quicker to activate than the in-built one.

An issue I found only on the desktop browser is that the highlighted text would jump ahead of the actual text the extension is reading and it would continue reading the text even if you press 'stop' (only in the case of the jumping highlighted text). Found that if this happens, press 'test' in the settings and the 'stop' after and it'll stop. Kind of annoying though since it happens every so often.

On the other hand, the mobile version of the extension is kinda meh. The issue I mentioned before doesn't seem to exist on mobile but a different one cropped up. On certain sites, or pages within the sites, the TTS randomly decides to change their voice to another. Again, only microsoft zira is listenable so it forces me to just stop the TTS and read manually.

Also, the 'sign in to use premium voices' have never acutally worked for me on mobile. Every time I click 'sign in', nothing appears T_T, lowkey frustrating. And apart from the offline voices, all of the voices don't work when I'm running on data. They do work when I'm using someone elses hotspot tho :(. Frustrating since I usually want to use mobile TTS when I'm out and about.