My mouse pointer does not change shape depending on what's under it on the screen. Strangely, this seems to happen only in Firefox and Chrome, but maybe I simply haven't noticed this problem in other apps. For example, when I load a new page in Firefox and the pointer is in the address bar, it changes to a text cursor, i.e., a vertical bar. Then I can move it all over the window, and it does not change when the mouse is passing over links, buttons, etc. Other times it can change to a hand or an arrow and then again it does not react to its context. In Chrome it happened before that when the pointer passed over the window edge it turned into a double arrow and then stayed this way regardless of its position, but I can't reproduce this at the moment. This happens often but is sometimes hard to reproduce exactly.
In other programs programs the pointer seems to behave normally. For example, in gedit it's a vertical bar inside the window and an arrow over the title bar or menu. In yelp (help application) the cursor is a vertical bar over text, an arrow over empty space and a hand over links. The pointer changes into an arrow when it leaves Firefox or Chrome and then stays this way when it is moved back inside.
In Chrome and Firefox I have fresh profiles without any customization or addons. I am using Ubuntu 19.04 with Wayland and Yaru theme for applications, cursor and icons in gnome-tweaks, but the issue seems to occur in other themes as well.
Edit. It seems that this is a Wayland issue because it does not happen when I log in using X11.
Best Answer
I have the same problem with Firefox 80.0.1 on Ubuntu 20.04.1 since two days. For testing I also installed Chrome which shows the same behavior. As long as I can say, no other programs seem to be affected. The mouse cursor often is stuck in its last state, mostly resize when moved into the window, but sometimes other cursors also. No matter if it is an arrow or another curser, it doesn't change on mouseOver on Webpages e.g. above links or in input boxes. Rebooting and changing the mouse don't solve the problem.
The perpetrator seems to be the Gnome extension "Soft brightness". Maybe the alpha-layer it puts over the screen to darken it interferes with the layer the browsers operate on and the layers the mouse is working on. Disabling this extension seems to solve the problem.