diff --git a/dev-libs/nspr/Manifest b/dev-libs/nspr/Manifest
index 49d2132cb6146..b83f64482b345 100644
--- a/dev-libs/nspr/Manifest
+++ b/dev-libs/nspr/Manifest
@@ -1,3 +1,4 @@
 DIST nspr-4.36.tar.gz 1036274 BLAKE2B 369d851db0f425f0c6c3cdaeb333320860b77b49b40b77cc983998de3f9128f9d987f143e9f2ce155d609fb23f3f9ed0d0abe7d74e20c59763e2b9bdd1835817 SHA512 55d21e196508ad29a179639fc8006f44b04dc2c0b5a85895e727f0a4f0ea37aeeceb936e37ac6b271b882a18e9f06d96133a60f19cee6345f8424c1c66e270ee
 DIST nspr-4.38.2.tar.gz 1025394 BLAKE2B 1e677504bed875651d7204d6df1a0f9671233bdab5a7b7cfdd691084c16c31a74a1126569372e4fe59edc8318b622551f979fbe55c8e64df1d977dbd63962cac SHA512 f17302b0973ab006f9e6af70199ac6bb40d6266f96ab4d6692f56c24979907a7f0a20cf9d926aa80084f2e0ce7dfd56de89a7547b5e7e8caafa7afa5eb0b7bd8
 DIST nspr-4.39.tar.gz 1014093 BLAKE2B dfb8a050ee29974d5226c4140901ba1704af9ddf6939053e495cf698b23c2eb2aff4fec968cb321648ea4cb373cd85cb81283693b11d2b761e3dcc85294dfa57 SHA512 201627666814552e3c98f66a0bdb18194670dcbdbc8cf3241079d918891d46aef1b10e9339beb84802d1de4189993340febab27344e97f8de21ceb1f43c77bda
+DIST nspr-4.40.tar.gz 1008989 BLAKE2B 91fcb301f001068190c9a0e0c792d7decb46bc56c26a7f2b0001aa4b322c71d2bfaecfa7f3467befb7ec1dfecd31694f164cdc3f1c49abcc30c3859896e3f1ac SHA512 7b1256da87e85287f4e2dab1ea735459044c258831f186bc662640c11ab0d96c8e28cd618ea6cb5178cf185e928c2dd967131154327a3bcb0d2ebdb7d560dff2
diff --git a/dev-libs/nspr/nspr-4.40.ebuild b/dev-libs/nspr/nspr-4.40.ebuild
new file mode 100644
index 0000000000000..03eea63a23797
--- /dev/null
+++ b/dev-libs/nspr/nspr-4.40.ebuild
@@ -0,0 +1,160 @@
+# Copyright 1999-2026 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+inherit autotools flag-o-matic toolchain-funcs multilib-minimal
+
+MIN_PV="$(ver_cut 2)"
+
+DESCRIPTION="Netscape Portable Runtime"
+HOMEPAGE="https://www.mozilla.org/projects/nspr/"
+SRC_URI="https://archive.mozilla.org/pub/nspr/releases/v${PV}/src/${P}.tar.gz"
+
+LICENSE="|| ( MPL-2.0 GPL-2 LGPL-2.1 )"
+SLOT="0"
+KEYWORDS="~alpha ~amd64 ~arm ~arm64 ~hppa ~loong ~m68k ~mips ~ppc ~ppc64 ~riscv ~s390 ~sparc ~x86 ~x64-macos ~x64-solaris"
+IUSE="debug"
+
+MULTILIB_CHOST_TOOLS=(
+	/usr/bin/nspr-config
+)
+
+PATCHES=(
+	"${FILESDIR}"/${PN}-4.7.1-solaris.patch
+	"${FILESDIR}"/${PN}-4.8.4-darwin-install_name.patch
+	"${FILESDIR}"/${PN}-4.8.9-link-flags.patch
+	# We do not need to pass -L$libdir via nspr-config --libs
+	"${FILESDIR}"/${PN}-4.9.5_nspr_config.patch
+)
+
+QA_CONFIGURE_OPTIONS="--disable-static"
+
+src_prepare() {
+	cd "${S}"/nspr || die
+
+	default
+
+	if use elibc_musl; then
+		eapply "${FILESDIR}"/${PN}-4.21-ipv6-musl-support.patch
+		eapply "${FILESDIR}"/nspr-4.35-bgo-905998-lfs64-musl.patch
+	fi
+
+	# rename configure.in to configure.ac for new autotools compatibility
+	if [[ -e "${S}"/nspr/configure.in ]] ; then
+		einfo "Renaming configure.in to configure.ac"
+		mv "${S}"/nspr/configure.{in,ac} || die
+	else
+		elog "configure.in rename logic can be removed from ebuild."
+	fi
+
+	# We must run eautoconf to regenerate configure
+	eautoconf
+
+	# make sure it won't find Perl out of Prefix
+	sed -i -e "s/perl5//g" "${S}"/nspr/configure || die
+
+	# Respect LDFLAGS
+	sed -i -e 's/\$(MKSHLIB) \$(OBJS)/\$(MKSHLIB) \$(LDFLAGS) \$(OBJS)/g' \
+		"${S}"/nspr/config/rules.mk || die
+}
+
+multilib_src_configure() {
+	# -Werror=strict-aliasing
+	# https://bugs.gentoo.org/867634
+	#
+	# Testsuite-only issue. Still, this makes it challenging to test the package with LTO
+	# enabled...
+	append-flags -fno-strict-aliasing
+	filter-lto
+
+	# The build system overrides user optimization level based on a configure flag. #886987
+	local my_optlvl=$(get-flag '-O*')
+
+	# bgo #923802
+	append-lfs-flags
+
+	# We use the standard BUILD_xxx but nspr uses HOST_xxx
+	tc-export_build_env BUILD_CC
+	export HOST_CC=${BUILD_CC} HOST_CFLAGS=${BUILD_CFLAGS} HOST_LDFLAGS=${BUILD_LDFLAGS}
+	tc-export AR AS CC CXX RANLIB
+	[[ ${CBUILD} != ${CHOST} ]] \
+		&& export CROSS_COMPILE=1 \
+		|| unset CROSS_COMPILE
+
+	local myconf=( --libdir="${EPREFIX}/usr/$(get_libdir)" )
+
+	# Optimization is disabled when debug is enabled.
+	if use debug; then
+		myconf+=( --enable-debug )
+	else
+		myconf+=( --disable-debug )
+		myconf+=( --enable-optimize="${my_optlvl}" )
+	fi
+
+	# The configure has some fancy --enable-{{n,x}32,64bit} switches
+	# that trigger some code conditional to platform & arch. This really
+	# matters for the few common arches (x86, ppc) but we pass a little
+	# more of them to be future-proof.
+	case $(tc-get-ptr-size) in
+		4) use abi_x86_x32 && myconf+=( --enable-x32 );;
+		8) myconf+=( --enable-64bit );;
+	esac
+
+	# Ancient autoconf needs help finding the right tools.
+	LC_ALL="C" ECONF_SOURCE="${S}/nspr" \
+	ac_cv_path_AR="${AR}" \
+	ac_cv_path_AS="${AS}" \
+	econf "${myconf[@]}"
+}
+
+multilib_src_test() {
+	# https://firefox-source-docs.mozilla.org/nspr/running_nspr_tests.html
+	cd "${BUILD_DIR}/pr/tests" || die
+	einfo "Building tests"
+	emake
+
+	einfo "Running test suite"
+	../../../${P}/${PN}/pr/tests/runtests.pl | tee "${T}"/${ABI}-tests.log
+
+	# Needed to check if runtests.pl itself or the tee (somehow) failed
+	# (can't use die with pipes to check each component)
+	[[ ${PIPESTATUS[@]} == "0 0" ]] || die "Tests failed to run!"
+
+	local known_failures=(
+		# network-sandbox related?
+		cltsrv
+		# network-sandbox related?
+		gethost
+	)
+
+	local known_failure
+	for known_failure in "${known_failures[@]}" ; do
+		sed -i -e "/${known_failure}.*FAILED/d" "${T}"/${ABI}-tests.log || die
+	done
+
+	# But to actually check the test results, we examine the log.
+	if grep -q "FAILED" "${T}"/${ABI}-tests.log ; then
+		die "Test failure for ${ABI}!"
+	fi
+}
+
+multilib_src_install() {
+	# Their build system is royally confusing, as usual
+	MINOR_VERSION=${MIN_PV} # Used for .so version
+	emake DESTDIR="${D}" install
+
+	einfo "removing static libraries as upstream has requested!"
+	rm "${ED}"/usr/$(get_libdir)/*.a || die "failed to remove static libraries."
+
+	# install nspr-config
+	dobin config/nspr-config
+
+	# Remove stupid files in /usr/bin
+	rm "${ED}"/usr/bin/prerr.properties || die
+
+	# This is used only to generate prerr.c and prerr.h at build time.
+	# No other projects use it, and we don't want to depend on perl.
+	# Talked to upstream and they agreed w/punting.
+	rm "${ED}"/usr/bin/compile-et.pl || die
+}