Gentoo's Bugzilla –
Attachment 595810 Details for
Bug 699890[mozilla overlay] www-client/firefox-71.0_beta8 should depend on >=dev-libs/nspr-4.23 - configure:8031: checking for NSPR - version >= 4.23 // configure: error: you do not have NSPR installed or your version is older than 4.23.