meta: move firedfox to Collaborator Emeriti list

They confirmed in email that they were fine with being moved to
Collaborator Emeritus and hope to be back contributing again soon.

PR-URL: https://github.com/nodejs/node/pull/27618


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>