When viewing open tabs on Firefox Android, the size of the tap target for the X button is small, which results in mis-taps. For example, when trying to tap the X button on a tab, I often accidentally tap on the tab itself, re-opening it instead.
A similar issue occurs with the pause button that appears on a tab that is currently playing media.
Making the size of the row at the top of a tab slightly taller, and increasing the size of the tap target for the X button, would make it easier to close a tab.