I think money spent on VPN and mdn+ goes more directly to funding Mozilla. But I would actually prefer to see a Mozilla that tries to become fiscally independent of partnerships like Google and fully commit to the donation model (+ maybe selling a few products like VPN and mdn+) closer to what Wikipedia is doing.
Money donated to Mozilla isn't used to develop Firefox: https://foundation.mozilla.org/en/
I'd be fine paying or donating to help Firefox development, but I can't.