Firefox is developed by the Mozilla Corporation, which is owned by the Mozilla Foundation. The corporation can send money to the foundation but not the other way around.

Here’s a really nice thread on Hacker News where they dig into the financial statements from the Mozilla Foundation. Also, here's a link to Mozilla’s FAQ where it vaguely mentions how Firefox funding works.

I find myself using Brave for most things currently but I do still use Firefox. I usually end up switching my primary between the two every couple of months.

Here’s an Ars Technica article talking about it.

OVH US has unlimited traffic but limits the bandwidth. I think they start at 100mbps and go over 1gbps depending on which configuration you pick.