Custom application launcher in Gnome 3

Hi all
I want to have a custom application launcher for firefox and chromium by which I would run the applications using “optirun”.

I thought it was enough to hack the firefox.desktop file presents in


as I update the key

Exec=/usr/bin/optirun firefox %u

no icon of firefox appears in the Gnome 3

Copy the desktop file to ~/.local/share/applications and modify as required, then run;

update-desktop-database ~/.local/share/applications/

I would call the file say firefox_optirun.desktop

thank you it works, but only as su.
I run

sudo update-desktop-database 

and put the desktop file in /usr/share/applications/

because running the user version

update-desktop-database ~/.local/share/applications/

didn’t have any effect