Disable the Selection API wot Turistu

disable parts of the Selection API which could be used to pastejack you (and execute arbitrary code on your machine) while using firefox on an X11 system.

see https://github.com/turistu/odds-n-ends/blob/main/firefox/pastejack.md#workaround

WARNING: this will break a lot of sites, including discussions in github.

OF COURSE, this does NOT access any of your data on any website. It's just that firefox's permissions are totally retarded. This temporary kludge may be broken or pointless, but one thing it's certainly not: it's not "accessing" any of your data.