While writing this issue, I discovered that this was an issue with drag and drop in Firefox. I fixed it by dragging and dropping another tab (in the default tab bar). One of the symptoms was that the blue drag-and-drop line was sometimes visible in the tab bar.
Abstract
TST sometimes switches to another tab, without me picking that tab.
Steps to reproduce
I've found two ways to reproduce this:
With the below tab list, it switches to https://wiki.gentoo.org/wiki/Category:Pages_with_template_loops.
Environment
While writing this issue, I discovered that this was an issue with drag and drop in Firefox. I fixed it by dragging and dropping another tab (in the default tab bar). One of the symptoms was that the blue drag-and-drop line was sometimes visible in the tab bar.