Users attempting to find the 8x8 Web Dialer extension (or 8x8 Click2Dial) for Mozilla Firefox web browser will not see any 8x8 products listed in Mozilla's marketplace, so the 8x8 Web Dialer cannot be installed in Firefox.
8x8 Web Dialer, 8x8 Click2Dial (legacy plugin), Firefox
Mozilla's policy regarding browser extensions effectively states that "the core functionality must be available free of charge, even after a potential trial. This is also the case if the add-on itself is free, but only works with a paid product."
As with many service providers, Mozilla removed the Web Dialer extension from its library in May of 2017.
The permanent solution is to use Web Dialer in the Google Chrome web browser.
All 8x8 browser extensions for Chrome, including Web Dialer, can be found here.