Why the Zen Browser Can’t be my Default Browser

Lately, I have been watching some videos extolling the Zen Browser, so I downloaded it to give it a try. Unfortunately, I ran into a problem almost immediately while using the YouTube feed in Inoreader. When I am scrolling through my YouTube feed for any videos I want to save in YouTube, I hit the Watch Later button that is embedded in the player next to the share button. The video is then automatically added to my watch later Que in Youtube. Unfortunately, that button doesn’t exist in the Zen Browser. This appears to be an issue on all browsers that are based on Firefox. Does anyone know of a solution for this problem because I would love to move away from a Chromium-based browser?