Hi @ayush222006,
I might be wrong about this, but I think it’s because there isn’t a $BROWSER environment variable set. Please open a terminal, and run the following:
echo $BROWSER
and provide the output here, wrapping it in 3 backticks (```) before and after the pasted text.
If confused, please see How to provide good information, specifically the section about pasting terminal output
I’m off now, but I suspect someone will be able to help further.
Hope you manage.