Firefox binary download version, how to get desktop icon?

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Hello,

I have download the mozilla version of firefox and unistalled the fedora one. I put the downloaded one in the current directory along with the .desktop file and:

sudo dnf remove firefox
mkdir "$HOME/bin"
cp -r ./firefox "$HOME/bin"
sudo cp firefox.desktop "$HOME/.local/share/applications"
sudo ln -s $HOME/bin/firefox/firefox /usr/local/bin/firefox

it works great BUT i can't find where to put the icon in the file system! its driving me mad, for example this does nothing:

sudo cp firefox.png /usr/share/icons/hicolor/256x256/apps

the desktop file merely says:

Icon=firefox

that tells me nothing! which file is the original icon that appears in search (repo installed), and where does it live? THANKS