Shadows And Title Color Cannot Be Disabled

In chrome/skin/prefs.css, there are a few verses like "text-shadow: 1px white" and "text-color: black".

Despite the leading comment ("Styles that can be modified via preferences"),
I cannot see the way to disable them via settings UI.

chrome/content/clrtabs.js shows that they are governed by "extensions.clrtabs.txtshadow" and "extensions.clrtabs.tabtextclr" preferences.

But, even if I set them to false and (blank), accordingly,
then invoke the settings UI and press OK, these lines do not vanish. The only way to get rid of them is edit prefs.css by hand - which works, until an update, that resets everything back.