The offline documentation from dmd has the favicon.ico file missing. It's needed to display the icon in the web browser. I manually fixed it just by downloading favicon.ico from https://dlang.org/favicon.ico to dmd2/html/d.

I don't know why favicon.ico isn't included in the offline documentation. Looking at the html files of the offline documentation in dmd2/html/d I see that there is a '<link rel="shortcut icon" href="favicon.ico">' tag which requests the favicon.ico file.

It only affects the offline documentation which is bundled with the dmd compiler. The equivalent online documentation doesn't have this issue.