diff --git a/firefox.spec b/firefox.spec
index 7324997..c6ee5f7 100644
--- a/firefox.spec
+++ b/firefox.spec
@@ -174,7 +174,7 @@ ExcludeArch: armv7hl
 Summary:        Mozilla Firefox Web browser
 Name:           firefox
 Version:        86.0
-Release:        4%{?pre_tag}%{?dist}
+Release:        5%{?pre_tag}%{?dist}
 URL:            https://www.mozilla.org/firefox/
 License:        MPLv1.1 or GPLv2+ or LGPLv2+
 Source0:        https://archive.mozilla.org/pub/firefox/releases/%{version}%{?pre_version}/source/firefox-%{version}%{?pre_version}.source.tar.xz
@@ -1081,6 +1081,9 @@ gtk-update-icon-cache %{_datadir}/icons/hicolor &>/dev/null || :
 #---------------------------------------------------------------------
 
 %changelog
+* Mon Mar 1 2021 Martin Stransky <stransky@redhat.com> - 86.0-5
+- Run xpcshell tests sequential
+
 * Mon Mar 1 2021 Martin Stransky <stransky@redhat.com> - 86.0-4
 - Enable Wayland backend only when Wayland display is set.
 
diff --git a/run-tests-x11 b/run-tests-x11
index 34f1a80..44b7e99 100755
--- a/run-tests-x11
+++ b/run-tests-x11
@@ -16,7 +16,7 @@ NCPUS="`/usr/bin/getconf _NPROCESSORS_ONLN`"
 # Basic render testing
 export TEST_PARAMS=""
 export TEST_FLAVOUR=""
-xvfb-run -s "$X_PARAMS" -n 94 ./mach xpcshell-test $TEST_PARAMS 2>&1 | cat - | tee $TEST_DIR/xpcshell
+xvfb-run -s "$X_PARAMS" -n 94 ./mach xpcshell-test --sequential $TEST_PARAMS 2>&1 | cat - | tee $TEST_DIR/xpcshell
 xvfb-run -s "$X_PARAMS" -n 99 ./mach reftest $TEST_PARAMS 2>&1 | tee $TEST_DIR/reftest$TEST_FLAVOUR
 xvfb-run -s "$X_PARAMS" -n 97 ./mach crashtest $TEST_PARAMS 2>&1 | tee $TEST_DIR/crashtest$TEST_FLAVOUR
 #xvfb-run -s "$X_PARAMS" -n 98 ./mach mochitest $MOCHITEST_PARAMS $TEST_PARAMS 2>&1 | tee $TEST_DIR/mochitest$TEST_FLAVOUR
@@ -24,7 +24,7 @@ xvfb-run -s "$X_PARAMS" -n 97 ./mach crashtest $TEST_PARAMS 2>&1 | tee $TEST_DIR
 # WebRender testing
 export TEST_PARAMS="--enable-webrender $TEST_PARAMS"
 export TEST_FLAVOUR="-wr"
-xvfb-run -s "$X_PARAMS" -n 93 ./mach xpcshell-test $TEST_PARAMS 2>&1 | cat - | tee $TEST_DIR/xpcshell-wr
+xvfb-run -s "$X_PARAMS" -n 93 ./mach xpcshell-test --sequential $TEST_PARAMS 2>&1 | cat - | tee $TEST_DIR/xpcshell-wr
 xvfb-run -s "$X_PARAMS" -n 96 ./mach reftest $TEST_PARAMS 2>&1 | tee $TEST_DIR/reftest$TEST_FLAVOUR
 xvfb-run -s "$X_PARAMS" -n 94 ./mach crashtest $TEST_PARAMS 2>&1 | tee $TEST_DIR/crashtest$TEST_FLAVOUR
 #xvfb-run -s "$X_PARAMS" -n 95 ./mach mochitest $MOCHITEST_PARAMS $TEST_PARAMS 2>&1 | tee $TEST_DIR/mochitest$TEST_FLAVOUR