Download the ZIP file then extract it and simply select Load unpacked from Browser extension page and select the extracted folder.
Download the CRX file then Simply open extensions page and select Load (.crx, .zip, .user.js) then select the CRX file.
The Firefox extension can only be installed in the Developer Edition, Nightly, and ESR versions of Firefox, after toggling the
xpinstall.signatures.required
preference in
about:config
then download the XPI file and open Add-ons manager then from settings click on Install add-on From File then select the XPI file.