Many thanks for your reply.
I have persevered by deleting parts of the webpage in my editor and re-doing them. As far as I can see the links were fine but I re-did them several times just to be sure. I had typed the track names into the page by cutting and pasting from a Word document but I deleted that and typed straight into the editor. That seems to have solved the IE problem.
Actually most of the problems are fixed, except the occasional time when the button does not show up against one particular track in Firefox. It’s ok for other browsers. It’s an intermittent problem but I can live with it. If the button does not show, then users can click on the hypertext link ok.