I am having the same problem with this https://addons.mozilla.org/es/firefox/addon/faviconizetab/
Except for the “auto faviconization” feature this is already available in Firefox. Just choose “Pin Tab” in the context menu. Other extensions are available for auto pinning: https://addons.mozilla.org/en-US/firefox/addon/autopintab/
PLEASE ALLOW THESE ONES I AM DESPERATE!!