When in the new tab page, hovering over an icon will reveal three dots. Click on this -> choose Edit. Now you can enter a custom image URL.

The suggestions were found, inititally

but I cannot locate a source for what the field is asking for.

URL's of located online icons don't seem to paste and addresses of icons in files do not populate teh field. I'm not sure what I am doing wrong and can't find a guide from FF/Moz that addresses this.

Thanks

You can only use images hosted on internet (http(s)://) and not local files (file://) links for the custom image.

Thanks, that helps some. At least I am looking in better places. The online files of icons I have located won't import. They seem to only have downloadable icons to save locally. Do you have a source of where icons that can be used (hosted ones) are found? Is it something each website handles on its own? How would they handle installing icons for browsers? I noticed that the sites that don't have homepage icons , don't get them for the address bar, with no clear pattern (eg certificates https). Same with my 1Password , ie no icons for those sites. I am looking for a Chase bank one , as my index case and am not sure where to look for icons I can use. Not a huge issue, it just seems that whatever the default is for my browser uses an video game that has insinuated itself as the default, and I don't want to erase the other ones by erasing them all, inadvertently.

Thanks again

Doesn't your ISP offer web space that you can use to host the image files ? Otherwise you can search the internet for image hosting websites. I don't know if it works if you access local files via localhost.

@cor-el Not sure what you are even talking about not helpful. Like asking me to find a way weave a powercord, when I was looking for a plug.