Firefox and Thunderbird are missing their icons

[RealMuffinTime]

These link do not work anymore:

https://ffp4g1ylyit3jdyti1hqcvtb-wpengine.netdna-ssl.com/addons/files/2015/11/get-the-addon.png

https://addons.cdn.mozilla.net/static/img/addons-buttons/TB-AMO-button_1.png