is it possible to post from lemmy to mastodon or vice versa?
5mon 4d ago by lemmy.ml/u/mouseirl in lemmy_support@lemmy.ml
You can post from Mastodon to Lemmy by putting a mention to the community name (like community@instance)
Mastodon users can follow the communities or the users.
So yes it pretty much works in both directions.
@mouseirl this answer is from my mastodon account.
Maybe it was the other way round. 
Yep! You see it from time to time.
Yes it is, but posts look like crap. I tried it once and mastodon is unreadable in Lemmy. I was criticized for it and deleted my post.
It isn't unreadable, you just need to keep in mind that the first line will be used as the post title. The Firefox community gets many Mastodon posts and most look ok