Currently, evolution and gaim-encryption are built against nspr-nss, while epiphany is built against mozilla.

Mozilla and Mozilla-firefox provide nspr and nss when placing their library directories in /etc/ld.so.conf. When you throw away nspr-nss on your system, gaim-encryption and evolution link against these libraries without any problem. If we place nss-nspr as build-dependencies in these packages and let it depend on nss, we could let the user choose if mozilla, mozilla-firefox or nss-nspr gets installed on the system (mozilla-thunderbird provides nss-nspr too BTW)

The same goes for epiphany/galeon: epiphany built against mozilla can run without problems against the libgtkmozembed libraries of firefox. Thunderbird also works, but that one has some nasty side-effects (forms posted are opened in a new page).