I'm-an-Idiot day (CSS)

i proposed below in passing
that the 13th of each month
should be "i'm an idiot day"

and bloggers on that day
should try to think of a question
they've hesitated to ask
for fear of looking stupid

and ask it publicly
in hopes that someone will answer
or that the act of asking will make it clearer
or will inspire the required research effort

so my idiot-question, a day early, is:

back when everyone on comp.infosystems.www.authoring.html
was promoting CSS stylesheets
their promise was that if i didn't like an author's page-design
i'd be able to substitute a different stylesheet

now i've got the latest version of firefox
but i don't see that function anywhere

(there's a page-style submenu under 'view'
but it doesn't offer any subtitutes)

so were we sold a bill of goods [yes]
or is this function still on its way
or what? [workaround]

(don't say greasemonkey-- that's javascript)

(sage does allow it,
globally for all rss-feeds)