I personally like to keep them separate as I use the different devices for different purposes. I don’t really ever have more than the visible row of bookmarks at any one time. If I need to save something I’m not using often, I’ll archive the page. Like for recipes in particular I have a directory filled with them.
I use Firefox focus for random browsing, normal Firefox for general browsing that I want to keep the history of, and Mull for anything where I want to absolutely minimize tracking / enhance privacy.