@fenn16: if you click the github page theres updates for this addon, they just havent bothered to update the opera extension hosted here.
https://github.com/ansh/jiffyreader.com/releases
The original creator has stopped supporting it, however there are people helping maintain its functionality.
This company claims to be selling fonts with that functionality.
https://reader.bionic-reading.com/products/font-customer
Also has a app on the windows store. I think the one time payment for the font is probably the way to go because the other thing is a subcription.