Help with finding icon names

[Ethan-Core2]

Recently found out you can use icons in dmenu mode with this syntax: echo -en "Firefox\0icon\x1ffirefox" | rofi -dmenu -no-config -show-icons.

However, the only one I can get to work is firefox. If I replace firefox with gimp, terminal, chromium etc, no icon shows up. I assume this is because those icons aren't in there by default. Is there a way to list all the icons you can use?

[DaveDavenport]

Rofi follows the following standard to find icons: https://specifications.freedesktop.org/icon-theme-spec/latest/

I don't directly know of an icon browser for this.