Apple never removed support for MTP. OSX doesn't support MTP in the OS directly.

What they apparently broke is Google's Android File Transfer program at http://www.android.com/filetransfer/ which no longer works properly under OSX 10.9. It contains it's own libmtp library and USB libraries.

In my experience of it, it never worked that well under previous releases of the OS either with official Android devices such as my Nexus 7 and an old HTC. It's been stuck at v1.0 since release.

I presume at some point Google will fix their app if possible but I don't see how Jolla can be relying on Google to fix an app so Jolla's customers can use a USB cable connection. On the N9 we had 'Nokia Link' on the Mac which wasn't too bad for a piece of Nokia Mac software. There were some complete stinkers over the years.