Imagine your friend that does not know anything about linux, don't you think this would make them not install the firefox flatpak and potentially think that linux is unsafe?
I ask this because I believe we must be careful and make small changes to welcome new users in the future, we have to make them as much comfortable as possible when experimenting with a new O.S
I believe this warning could have a less alarming design, saying something like "This app can use elevated permissions. What does this mean?" with the "What does this mean?" text as a clickable URL that shows the user that this may cause security risks. I mean, is kind of a contradiction to have "verified" on the app and a red warning saying "Potentially unsafe", the user will think "well, should I trust this or not??"
If you use Debian-based linux (Ubuntu, Minut, others), Mozilla recommends getting the package directly from their respository rather than flatpak or other repos.
Personally, I saw a major performance increase on my low-powered laptop when I switched from flatpak to the Mozilla package.
https://blog.mozilla.org/en/products/4-reasons-to-try-mozillas-new-firefox-linux-package-for-ubuntu-and-debian-derivatives/
I've tried both on my low powered HTPC and came to the same conclusion - especially noticeable where video acceleration is concerned