!Friendica Admins There are a lot of relay services out there in the fediverse. Problem only is that not all systems are participating. There's a nice service at relay.fedi.buzz/ that helps here. With this service you can create a feed that contains all posts from a given Mastodon server.
Also you can subscribe to tags with this service. This seems to work really fine with the current Friendica. I will create a small PR, but this will only handle some cosmetic issues.