Now that I think about it, you can probably just use:
Code:
/shell_open firefox
Or:
Try passing the parameter as a separate one. I bet you don't need to use those sepecial parameters.
Try copy/pasting this one:
Code:
/shell_open firefox https://www.google.com/search?q=drumsui
My guess is no spaces for the URL, and no surrounding quotes are required (might even break it)