And Donald Trump isn't an ally of Internet freedom - if anything, he's been in favor of letting social media companies para-censor what they want. He called Net Neutrality "Obamacare for the Internet", so he clearly also doesn't care if Comcast censors things. Furthermore, the GOP has traditionally been in favor of "private companies can say what they want and you should have no legal recourse for that". As far as I'm concerned, him getting banned from Twitter was him getting hoist by his own petard.

There's also the related problem that any reasonable free speech protections that apply to private fora would almost certainly not have protected Trump here. Twitter had an explicit policy of letting Trump off the hook for things that would ordinarily get you banned, even things like copyright violations. (Yes, Donald Trump and Donald Trump alone had DMCA immunity.) If we had regulated Twitter like a common carrier, they wouldn't have been allowed to have this two-tiered world leaders policy. So Trump would have been banned in 2017 instead of 2021.

I really can't think of a way in which Trump stays on Twitter without some massive intrusion into the way the Internet runs. Either you...

1. Require private fora to not have any speech rules - in which case we turn the entire Internet into USENET/4chan and anyone not as spammy/toxic is para-censored by being talked over

2. Require private fora to not enforce speech rules against world leaders - in which case you've taken away the platform's right to free association without any of the benefits of common carrier regulation

I don't see how either of those improve freedom online. Given that Mozilla's non-profit arm has a stated goal of protecting user freedom, it's perfectly reasonable for them to not have any particular sympathies for Mr. "Obamacare for the Internet". The best Mozilla can do - and what they actually did - is argue for transparency and regulation on how social media companies use their power to shape public discourse.