Why are shortcut icons not correct on toolbar?

Screen shot of the error?

Few of my shortcut icons on toolbar have been replaced with a google "G" or a round gray and white circle and not the official logo for the website. There is the firefox fox/globe logo on toolbar, fb logo, UPS, youtube, etc correct logos icon. Five of my shortcuts have a "G" or the white and gray circle. Previously/originally had correct icon logo. Why?

Do you try to look at their properties and attempt to change or modify them?

How would you change or modify the properties?

Check out this answer => https://support.mozilla.org/questions/1172961