You need to create a jojo.desktop file. In the editor, for example:
gedit ~/.local/share/applications/jojo.desktop
and paste:
[Desktop Entry]
Name=jojo
Comment=Browse the Web
Exec=/path/to/JoJo.AppImage
Icon=/path/to/jojo.svg
Type=Application
Categories=Network;WebBrowser;
MimeType=text/html;text/xml;application/xhtml+xml;application/vnd.mozilla.xul+xml;text/mml;x-scheme-handler/http;x-scheme-handler/https;
I couldn't find the icon on the internet, but if you want to experiment with it, download JoJo as the Source code (.tar.gz) and extract the icon."
Then:
xdg-mime default jojo.desktop x-scheme-handler/http
xdg-mime default jojo.desktop x-scheme-handler/https
Check: xdg-mime query default x-scheme-handler/http
.
