https://addons.mozilla.org/en-US/firefox/addon/reload-in-add...
Or you can use the "double tap the dots menu" trick.
You might like it, though. I've used Brave's mobile sync and it works for bookmarks across devices quite well. It's surprisingly simple to set up, too. I don't fret much about forgetting whether I opened a tab on my phone or desktop if I remember to bookmark it.
That said, I still use KDE connect to send links to my primary Firefox instance and vice-versa, but the bookmark sync is in some ways more convenient. I'd imagine they'll eventually synchronize more things, like tabs.
The same happens when some sites require Chrome to work, blocking all the rest. In 2019 it's unacceptable
Because it's 100% just a missing feature in Firefox mobile, there's nothing website developers should add to "make it work" on it.