Tablets do use on-screen keyboards, not really a keyboard like they were in the oldies, but hey maybe you are doing something wrong here or it could be something else. I have a tablet to and once I bought a real keyboard just for fun, do what you like. Did I gave you some usefull information, I hope so because my fingers hurt so much right now.

Im having the same issue. When in tablet mode, the OSK doesn't pop up when selecting text entry, and if I force it to using the task bar, it immediately hides. Chrome and Edge don't have this issue.

My current work around is to put the OSK into the floating mini keyboard mode, and manually open it when needed, which is a pain in the butt.

Sadly this issue has been around for over a year, and no updates. Concerning given that every manufacturer has a Windows tablet these days, and Microsoft considers the Surface to be the de facto Windows experience.

https://bugzilla.mozilla.org/show_bug.cgi?id=1645571

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