the currently used version of gecko-sdk is not that used in the new build of firefox 1.5 and up, thus anyplugins which are built agaisnt the sdk for firefox cause a crash in firefox when the plugin is loaded.
My opinion: mozilla firefox and thunderbird 1.5 are known to also break calendar support and at least mozilla firefox has a lot of problems, they should better stay masked. Fine working xorg-x11 modular on the other side is a candidate for unmasking in testing.
I have yet to see which plugins you speak of. Maybe instead of ranting about what you believe should happen you could provide the appropriate information to help you correct your problem? Emerge info is all required on every bug that is filled re-open the bug with emerge info.