diff --git a/binary_tarball/scripts/3_Configure_Source_Code.sh b/binary_tarball/scripts/3_Configure_Source_Code.sh
index 1707ebd..e912c92 100755
--- a/binary_tarball/scripts/3_Configure_Source_Code.sh
+++ b/binary_tarball/scripts/3_Configure_Source_Code.sh
@@ -24,12 +24,16 @@ ac_add_options --enable-application=browser
 ac_add_options --with-libclang-path="/usr/lib/llvm-9/lib"
 ac_add_options --with-clang-path="/usr/bin/clang-9"
 
+# let's see if this works: make things backwards-compatible as much as possible
+# TODO: check if this would also work when building on something newer to have it run on
+# 16.04/xenial later on as well?
+ac_add_options --enable-stdcxx-compat
+
 # This supposedly speeds up compilation (We test through dogfooding anyway)
 ac_add_options --disable-tests
 ac_add_options --disable-debug
 
-# might cause issues for appimage/flatpak, so keep it unset
-# ac_add_options --prefix=/usr
+ac_add_options --prefix=/usr
 ac_add_options --enable-release
 ac_add_options --enable-hardening
 ac_add_options --enable-rust-simd
@@ -84,6 +88,7 @@ export CXXFLAGS+=" -g0"
 export RUSTFLAGS="-Cdebuginfo=0"
 
 # from ALARM
+# See https://bugzilla.mozilla.org/show_bug.cgi?id=1430094
 ac_add_options --disable-webrtc
 
 END
diff --git a/binary_tarball/scripts/4_Build_Binary_Tarball.sh b/binary_tarball/scripts/4_Build_Binary_Tarball.sh
index f393cfa..d7649e4 100755
--- a/binary_tarball/scripts/4_Build_Binary_Tarball.sh
+++ b/binary_tarball/scripts/4_Build_Binary_Tarball.sh
@@ -53,52 +53,52 @@ cargo install cbindgen
 rm -f mozconfig
 
 # Do 3-tier PGO
-# echo "Building instrumented browser..."
+echo "Building instrumented browser..."
 
-# if [[ $CARCH == 'aarch64' ]]; then
-#
-# cat >.mozconfig ${CI_PROJECT_DIR}/mozconfig - <<END
-# ac_add_options --enable-profile-generate
-# END
-#
-# else
-#
-# cat >.mozconfig ${CI_PROJECT_DIR}/mozconfig - <<END
-# # -fno-plt with cross-LTO causes obscure LLVM errors
-# # LLVM ERROR: Function Import: link error
-# # CFLAGS="${CFLAGS/-fno-plt/}"
-# # CXXFLAGS="${CXXFLAGS/-fno-plt/}"
-#
-# ac_add_options --enable-profile-generate
-# END
+if [[ $CARCH == 'aarch64' ]]; then
 
-# fi
+cat >.mozconfig ${CI_PROJECT_DIR}/mozconfig - <<END
+ac_add_options --enable-profile-generate
+END
+
+else
+
+# -fno-plt with cross-LTO causes obscure LLVM errors
+# LLVM ERROR: Function Import: link error
+CFLAGS="${CFLAGS/-fno-plt/}"
+CXXFLAGS="${CXXFLAGS/-fno-plt/}"
+
+cat >.mozconfig ${CI_PROJECT_DIR}/mozconfig - <<END
+ac_add_options --enable-profile-generate=cross
+END
+
+fi
 
 # Executes the actual build
-# printf "\nBuilding LibreWolf\n";
-# ./mach build;
+printf "\nBuilding LibreWolf\n";
+./mach build;
 
-# echo "Profiling instrumented browser..."
-# ./mach package
-# LLVM_PROFDATA=llvm-profdata \
-  # JARLOG_FILE="$PWD/jarlog" \
-  # xvfb-run -s "-screen 0 1920x1080x24 -nolisten local" \
-  # ./mach python build/pgo/profileserver.py
-#
-# if [[ ! -s merged.profdata ]]; then
-  # echo "No profile data produced."
-  # exit 1
-# fi
-#
-# if [[ ! -s jarlog ]]; then
-  # echo "No jar log produced."
-  # exit 1
-# fi
-#
-# echo "Removing instrumented browser..."
-# ./mach clobber
-#
-# echo "Building optimized browser..."
+echo "Profiling instrumented browser..."
+./mach package
+LLVM_PROFDATA=llvm-profdata \
+  JARLOG_FILE="$PWD/jarlog" \
+  xvfb-run -s "-screen 0 1920x1080x24 -nolisten local" \
+  ./mach python build/pgo/profileserver.py
+
+if [[ ! -s merged.profdata ]]; then
+  echo "No profile data produced."
+  exit 1
+fi
+
+if [[ ! -s jarlog ]]; then
+  echo "No jar log produced."
+  exit 1
+fi
+
+echo "Removing instrumented browser..."
+./mach clobber
+
+echo "Building optimized browser..."
 
 if [[ $CARCH == 'aarch64' ]]; then
 
@@ -114,6 +114,10 @@ END
 else
 
 cat >.mozconfig ${CI_PROJECT_DIR}/mozconfig - <<END
+ac_add_options --enable-lto=cross
+ac_add_options --enable-profile-use=cross
+ac_add_options --with-pgo-profile-path=${PWD@Q}/merged.profdata
+ac_add_options --with-pgo-jarlog=${PWD@Q}/jarlog
 ac_add_options --enable-linker=gold
 END