Some websites do not serve a favicon, or Firefox seems to not pull one (not sure which). Regardless, when without a favicon, Firefox should use a placeholder icon to keep tab bar consistency. When a tab doesn't have a favicon, it makes it a bit more difficult to find when searching along the tab bar, and makes it more difficult to delineate where the tabs are separated. Since Firefox already has a "globe" icon used in the bookmarks manager, I would think it would be easy to use that to indicate a webpage. AFAIK, Firefox is the only browser that doesn't do this.
I have attached a screenshot showing how it looks next to a tab with a favicon.
Thanks for reading!
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