TinyMCE style issue in Firefox (not IE)

Hi all

I have a TinyMCE install on Drupal 4.8, and it works fine, except we have recently discovered that custom styles (as defined in the "CSS classes" section of the TinyMCE settings page) aren't working as well as they should in Firefox. It works fine in IE.

I can select some text, and choose a style from the dropdown, and it will apply correctly using a span tag. However, if I select an image, and choose a style, the image will flash (so some JS is doing something) but otherwise the img tag is left unmodified. I am sure this used to work, so I wonder if a clash with something else (eg the jquery47 module) may be to blame? However, I don't get any JS errors reported at all in Firebug, which one would expect if a clash was occuring.

If it helps answer the question, the TinyMCE JS code that is executed is thus:

tinyMCE.execInstanceCommand('mce_editor_0','mceSetCSSClass',false,'imgborder');

where 'imgborder' is the css class name to be applied, presumably to the currently selected xhtml. I will have to find this code and try to trace it (not looking forward to that!) but if in the meantime readers have suggestions, I would be very pleased to hear them.