I use Reddit and instagram on mobile browsers, they seem fine for a few missing features and nagging you to use the app.
There is a seemingly persistent bug where reddit fails to remember preferences surrounding mobile/desktop and old/redesign. Sometimes you will click a link and the page it delivers you to will be on the mobile site, sometimes it will take you to the redesign. It's been going on for at least a year. I use reddit a lot and I run into it at least every week. Sometimes it sticks and I have to relog to get my preferences back.
Firefox for Android prevents such attempts by default. That, plus uBlock Origin with its integrated element picker to permanently block elements make reddit bearable.