I have a reasonable question for a self-indulgent reason. I wanted to know more about the custom icon that sometimes appears next to the URL in the browser's address bar. (If unspecified, it is just a generic browser file icon.)

First of all, what is the icon called? "Site icon" or "URL icon" or something else?

How is the icon which is used determined?

Is it done per-page, like any other image, or per site, like a cookie?

I imagine that in HTML, it would belong in the header, but I haven't been able to find anything. Are they .ico files?

On the browser's client machine, where are these images stored?

Is it in the web cache like images in pages or in a special place, similar to cookies?

Some of my saved links retain the icon, some don't. The icons for saved bookmarks/favorites sometimes last a while, then disappear, leading me to believe that they probably are stored in the web cache. Might there be a way for me to save the icon with other Windows apps icons elsewhere so that they persist after I empty my web cache?

It would depend on if the browser looks outside the cache for .ico files, but at the crudest, I could write a .BAT file to copy them back into my web cache after I empty it.

Are "URL icons" supported by all browsers?

I would like it if my Favorites/Bookmarks menu would retain these icons; they make it visually easier to locate a specific link without actually reading the text for each one.