Can you tell us where this was so we can update this? (If this is our donation share, we've been asking them to add Mastodon for a while, but they haven't been able to yet.)

I paid money to support Thunderbird:
First of all there were this four buttons on your web interface (I couldn't get a screen dumb). Same choices i got in the following email from give(at)thunderbird(dot)net.

Our donation processor has a lot of defaults as far as social platforms. We've been asking them about adding Mastodon for a while now, but so far they haven't been able to. But we'll keep asking!