Firefox is falling to pieces and I have very good reason to suppose they are now dependent on Google for much of their programming - though nobody has said this is the case to my knowledge. It ought to be possible to adjust for that, and for any other browser that causes issues by not doing what the CSS specifications say they should do.
Looking at the comments, clearly there are plenty of other places where this is a problem and I can take a look at those when the feeding game is over.
Our first priority must be to ensure beginners know what the buttons are for, and thus fixing other troublesome positioning must have higher priority than an on/off button. Once that has been done, an on/off button will depend on Al's availability, because there are some very complex issues involved in getting it *right*, rather than making something that will work in some cases some of the time.
I'm grateful for all the comments, as the whole purpose of hovered text is to make the game simpler to use, and when it stops doing that for experienced users, an on/off button is indicated. The point is to provide service, not tell ourselves how clever we are. 'We are not SGN'.
![Wink ;)](./images/smilies/icon_e_wink.gif)