c1b549e3ee
Per Product, we need to use a thumb-down icon for the best-match block button instead of the close `X`. We have a thumb-down icon already in browser/themes/shared/controlcenter/socialblock.svg. I checked with Ryan and that's the icon we should use here. This does the following: * Move the icon to browser/themes/shared/icons/thumb-down.svg * Update the sites where that icon is currently used * Use the icon for the best-match block button Differential Revision: https://phabricator.services.mozilla.com/D138551