Reeder is my RSS client of choice, especially since most browsers abandoned the "standard". It works well with Feedly, my Google Reader replacement.
MarsEdit is my WordPress authoring client of choice, especially as the WordPress native client is barely functional and Emacs' org2blog is a bit too fiddly for my time.
Since macOS Mojave (I prefer the incorrect Americanized pronunciation close to "mo' java" and not the more correct one near "mo' have, eh", because it's a buggy release & I still have room to grow as a person), these two tools no longer work well together.
Pre-Mojave, when I wanted to write about an article in Reeder I would click the icon for MarsEdit and the text magically appeared in a new MarsEdit post.
Now, I get an error.
I presume the problem is with the ever evolving security protections in Apple's macOS and that the author of Reeder hasn't updated for it yet.