Bugzilla

Here's a screencast showing Nightly 2021-04-25, where the cursor remains visible.  I captured this screencast with Ubuntu accessibility "zoom" feature enabled, so all the pixels are scaled up.

If you look closely, you can see that indeed the cursor is overlapping the spin buttons here (the buttons' leftmost column of pixels).

Here's a screencast showing Nightly 2021-04-25, where the cursor remains visible.  I captured this screencast with Ubuntu accessibility "zoom" feature enabled, so all the pixels are scaled up.

If you look closely, you can see that indeed the cursor is overlapping the spin buttons here (the buttons' leftmost column of pixels). So it makes sense that bug 1707070's change to the paint ordering would have caused the cursor to become invisible.