As soon as the OSK finishes the slide animation, Firefox resizes back to fill the screen.
As the OSK slides back down, Firefox appears to only fill half the screen and I can briefly see the desktop in the background.
Also a Surface Go 2 that used to work fine, but after update to 2004 (OS build 19041.388) now exhibits the described behavior in Firefox - as soon as the on-screen keyboard finishes sliding up into position, Firefox resizes, and the OSK disappears. I have a Surface Pro 6 with OS build 18363.959 that works fine in tablet mode. Looks like tablet mode had some changes introduced: Get search suggestions in the search bar and quickly access the sites you visit most. Firefox makes password management easy by remembering your passwords across devices. Sync your devices and send open tabs between mobile and desktop. This only started happening after update to Windows 10 2004. Add Firefox across your devices for secure, seamless browsing. The onscreen keyboard appears, and persists, until it is manually dismissed, the way it behaves in the new chromium based Microsoft Edge under the same circumstances. You cannot make the keyboard reappear until you 'tap' out of the text field, and then back in it again, when the onscreen keyboard once again exhibits the same behavior continuously and consistently. The onscreen keyboard appears, and then automatically dismisses itself as soon as the animation to appear is finished. I am running a Lenovo 元90 Yoga (2-in-1 laptop with wacom layer, and touchscreen) with up-to date Windows 10 build 2004, all Lenovo software/firmware up to date. The same is the case for Firefox Nightly 79.0a1 () (64-bit). 'Tap' any text entry field including but not limited to the address bar. Windows 10 running in tablet mode, with the taskbar 'auto-hide' setting enabled.