By doing so, could Mastodon users reach our instance?

Completely insane.

Just in case you didn’t know, there’s PeerTube, an ActivityPub-compatible software for video sharing ;-)

I really recommend AnySoftKeyboard.

Isn’t Tor browser based on Firefox?

Yep. I once heard on an IRC room about testing being “highly unrecommendable” because it could break at any time! I rolled my eyes. Testing branch is fully usable, and it rarely breaks if you are a mindful user.