thank you for your suggestions cor-el and jscher2000. i modifed my userContent.css file as shown ab

thank you for your suggestions cor-el and jscher2000. i modifed my userContent.css file as shown above by deleting the namespace line entirely, and also trying these entries:

@namespace url("http://www.w3.org/1999/xhtml"); and @namespace url(http://www.w3.org/1999/xhtml);

but none of these 3 variations changed the way the webpages which i visit every day looked and the headings were all the usual size they always have been.

i tried these 3 variations on a half dozen different sites, with no affect.

i also tried disabling the no-squint FF add-on, and i changed the FF content option to let the webpages display their own fonts and sizes rather than my selection, and then changed them back to display my fonts and sizes.

nothing i have done has been able to reach the font display.

i'll try anything else you can suggest.

after looking through the firebug app on several different web sites, it seems there are many levels of display controls/code elements which are able to affect the final appearance. i wonder how FF determines which of the controls to use in the final display. maybe there isn't any way to tell without close inspection of the source and FF configuration