For Chrome: I found with my Surface Pro 4, I had to enable the flags in Chrome itself to get touch capability. Even if Windows swaps from laptop to tablet mode, Chrome isn't smart enough to know when this occurs dynamically. Go to chrome://flags and change the "Enable Touch Events" setting from "Automatic" to "Enable", this should trigger Chrome to accept touch input. I don't think this actually activates tablet mode, but it does give you all of Roll20's functionality if you have the Surface stylus. I've found that with fingers, you can do most things on the VTT, but abilities like panning, moving tokens, and sometimes horizontal scrolling doesn't work with fingertips. They will work with the stylus, though. For Firefox, fingertips were registering without any issues on my Surface Pro. I didn't have to change the touch flags for it.
