you can manually compile mozilla-firefox to use gtk1 but there is no useflag for it. Reproducible: Always Steps to Reproduce: 1.emerge -va mozilla-firefox 2.notice that it dosent have gtk1 as a useflag 3.weep a bit
And there won't be any such flag, ever... gtk-1 is dead and unsupported upstream, and will be removed from the tree at some point, hopefully sooner than later. Sorry.