how to temporarily override page style/appearance ?

[martinko]

hi!

i'm looking for an easy way of changing an html page appearance in
mozilla/seamonkey browsers.
i know i can change default colours in preferences->appearance->colors
but that is global and permanent.
i'd rather have something like there's in opera where you can easily
apply user defined theme/stylesheet per window/tab.
is there a similar extension for seamonkey/mozilla pls ??

cheers,

martin