Well, despite the lack of account management section, they certainly aren't short on pages to donate money:
https://secure.anedot.com/firearmspolicycoalition/fpc?amount=25&source_code=donate
https://secure.anedot.com/firearmspolicycoalition/march2023_joingaw?sc=joingaw
https://secure.anedot.com/firearmspolicycoalition/join_the_fpc_grassroots_army?sc=joinfpc
https://secure.anedot.com/firearms-policy-foundation/quick_donate?sc=quick_donate
Also, don't fall into the trap of signing up without paying (yes you can find that along your adventure). That only puts you on the email distro, despite the site saying you're a supporter.
The support page seems to have some better details, it even has a renew link, which seems to be the same as the join link.
https://www.firearmspolicy.org/support
Note for anyone who may do work for FPC: Please, please, please go hire a UX person for a few months.