Spending most of my web time in Opera, I had noticed that on one of my PCs, hovering over a hypertext link (i.e.
<a href="..." ...>) had ceased displaying the target of the link in the UI, and there didn't seem to be a setting to make it appear again. Even when upgrading, that annoying behaviour kept stuck.
As one can expect, it turned out to be simple to fix, just not obvious in the Opera UI. Here is the procedure: