Install Unfriend Checker Firefox Addon for Facebook:

Latest version: 19, updated on Tuesday, February 25, 2020

Add-on is available for install on official addons.mozilla.org:
https://addons.mozilla.org/en-US/firefox/addon/unfriend-checker/

If above link is not available for any reason you can install this add-on manually following this steps:

Steps to install this add-on:

1. Download and unzip Unfriend Checker Firefox Addon archive (Click here to download)
1. Open Firefox menu
2. Click Add-ons or use CTRL+SHIFT+A or type in browser address bar about:addons
3. Select from Settings icon Install Add-on From File…
4. Load Unfriend Checker Firefox Addon xpi file.