Thanks to everyone for your responses; much appreciated.
I have been using both the latest nightly build of the NVDA screen reader, and also the System Access screen reader (latest update) for testing purposes.
Using a Toshiba Satellite P755 laptop running Windows 7 Home Premium.
My theme is the Genesis Serenity child theme. Latest versions of both Genesis and Serenity child theme.
Have tested on Firefox 26 and IE 11.
I think I'll disable all plugins next and see what, if anything, changes. Will report back.