Since I originally wrote this post, I have found an alternative for bookmark sync. I now use raindrop.io to sync my bookmarks across all my browsers.
It has extensions for Orion, Firefox, Chrome, and Safari. It also has mobile apps for iOS/Android, a web interface, and a desktop app.
This has mostly mitigated the issue with cross-browser bookmarks and has allowed me to use Orion as my primary browser on my MacBook! 🎉
The built-in functionality to migrate bookmarks from Firefox -> raindrop missed some things, so I did have to write a custom script to migrate correctly. However, aside from that, things are working flawlessly now 🙂
Hopefully, this can help someone trying to work across multiple browsers. Although I still think it would be very nice if this issue could be fixed (especially the history problem). It is encouraging that Firefox sync has an API 🙂