CSS directives for the selector "mtext[href]"

Dear Friends,

In connection with a MathJax discussion I took a look (with Firefox
14.0.1 in linux/ubuntu) at the following bit of CSS in the classical
XHTML+MathML scenario:

     mtext[href] {
       color: #B00000;
       text-decoration: underline ! important;
     }

It seems to be inert.  The matching elements are colored
blue, rather than red, and not underlined.

Any clues?

Might there be something marked !important in front of it?

Thanks.

                                    -- Bill