How do I launch Firefox with a negative nice value as a regular user?

I did this sudo nice -n -1 firefox to launch Firefox with higher priority and make all subprocesses that are executed at launch inherit that priority but it failed with an error message about Firefox can't be run as root in a regular user account. I need sudo to use negative nice values but the rest of the command should be run as my regular user. How can I use negative nice values but still run the program as my regular user? I don't want to use renice on already launched processes.