diff --git a/build-engine.sh b/build-engine.sh
index 92b9537..5afdcdd 100755
--- a/build-engine.sh
+++ b/build-engine.sh
@@ -25,39 +25,53 @@ ac_add_options --disable-clang-plugin
 ac_add_options --enable-jitspew
 ac_add_options --enable-optimize=-O3
 ac_add_options --enable-js-streams
+ac_add_options --disable-shared-memory
+ac_add_options --wasm-no-experimental
+ac_add_options --disable-wasm-extended-const
+ac_add_options --disable-js-shell
 ac_add_options --enable-portable-baseline-interp
+ac_add_options --disable-cargo-incremental
 ac_add_options --prefix=${working_dir}/${objdir}/dist
 mk_add_options MOZ_OBJDIR=${working_dir}/${objdir}
 mk_add_options AUTOCLOBBER=1
+
 EOF
 
-target="$(uname)"
-case "$target" in
-  Linux)
-    echo "ac_add_options --disable-stdcxx-compat" >> "$mozconfig"
-    ;;
+if [[ "$mode" == "release" ]]; then
+cat << EOF >> "$mozconfig"
+ac_add_options --enable-strip
+ac_add_options --disable-debug
+EOF
+else
+cat << EOF >> "$mozconfig"
+ac_add_options --enable-debug
+EOF
+fi
 
-  Darwin)
-    echo "ac_add_options --host=aarch64-apple-darwin" >> "$mozconfig"
-    ;;
+cat << EOF >> "$mozconfig"
+export RUSTFLAGS="-C relocation-model=pic"
+export CARGOFLAGS="-Z build-std=panic_abort,std"
+export CFLAGS="-fPIC"
+export CXXFLAGS="-fPIC"
 
-  *)
-    echo "Unsupported build target: $target"
-    exit 1
-    ;;
-esac
+EOF
 
-case "$mode" in
-  release)
-    echo "ac_add_options --disable-debug" >> "$mozconfig"
+# Note: the var name is chosen to not conflict with the one used by the toolchain
+OS_NAME="$(uname | tr '[:upper:]' '[:lower:]')"
+export OS_NAME
+
+case "$OS_NAME" in
+  linux)
+    echo "ac_add_options --disable-stdcxx-compat" >> "$mozconfig"
     ;;
 
-  debug)
-    echo "ac_add_options --enable-debug" >> "$mozconfig"
+  darwin)
+    echo "ac_add_options --host=aarch64-apple-darwin" >> "$mozconfig"
+    OS_NAME="macos"
     ;;
 
   *)
-    echo "Unknown build type: $mode"
+    echo "Can't build on OS $OS_NAME"
     exit 1
     ;;
 esac
@@ -65,8 +79,32 @@ esac
 
 # Ensure the Rust version matches that used by Gecko, and can compile to WASI
 rustup target add wasm32-wasi
+rustup component add rust-src
+
+# Ensure that the expected WASI-SDK is installed
+if [[ -z "${WASI_SDK_PREFIX:-}" ]]; then
+  sdk_url="$(sed "s/\$OS_NAME/$OS_NAME/g" "$script_dir/wasi-sdk-url")"
+  echo "WASI_SDK_PREFIX not set, downloading SDK from ${sdk_url} ..."
+  mkdir -p wasi-sdk
+  cd wasi-sdk
+  curl -LO "$sdk_url"
+  sdk_file="$(basename "$sdk_url")"
+  tar -xf "$sdk_file"
+  rm "$sdk_file"
+  WASI_SDK_PREFIX=$PWD/$(ls . | head -n 1)
+  export WASI_SDK_PREFIX
+  cd ..
+  echo "Downloaded and extracted. Using compiler and sysroot at ${WASI_SDK_PREFIX} for target compilation"
+else
+  if [[ ! -d "${WASI_SDK_PREFIX}" ]]; then
+    echo "WASI_SDK_PREFIX set, but directory does not exist: ${WASI_SDK_PREFIX}"
+    exit 1
+  fi
+  echo "WASI_SDK_PREFIX set, using compiler and sysroot at ${WASI_SDK_PREFIX} for target compilation"
+fi
 
-fetch_commits=
+# If the Gecko repository hasn't been cloned yet, do so now.
+# Otherwise, assume it's in the right state already.
 if [[ ! -a gecko-dev ]]; then
 
   # Clone Gecko repository at the required revision
@@ -76,46 +114,59 @@ if [[ ! -a gecko-dev ]]; then
   git -C gecko-dev remote add --no-tags -t wasi-embedding \
     origin "$(cat "$script_dir/gecko-repository")"
 
-  fetch_commits=1
-fi
-
-target_rev="$(cat "$script_dir/gecko-revision")"
-if [[ -n "$fetch_commits" ]] || \
-  [[ "$(git -C gecko-dev rev-parse HEAD)" != "$target_rev" ]]; then
-  git -C gecko-dev fetch --depth 1 origin "$target_rev"
-  git -C gecko-dev checkout FETCH_HEAD
+  target_rev="$(cat "$script_dir/gecko-revision")"
+  if [[ "$(git -C gecko-dev rev-parse HEAD)" != "$target_rev" ]]; then
+    git -C gecko-dev fetch --depth 1 origin "$target_rev"
+    git -C gecko-dev checkout FETCH_HEAD
+  fi
 fi
 
-# Use Gecko's build system bootstrapping to ensure all dependencies are
-# installed
+## Use Gecko's build system bootstrapping to ensure all dependencies are
+## installed
 cd gecko-dev
 ./mach --no-interactive bootstrap --application-choice=js --no-system-changes
 
-# ... except, that doesn't install the wasi-sysroot, which we need, so we do
-# that manually.
-cd ~/.mozbuild
-python3 \
-  "${working_dir}/gecko-dev/mach" \
-  --no-interactive \
-  artifact \
-  toolchain \
-  --bootstrap \
-  --from-build \
-  sysroot-wasm32-wasi
-
 cd "$working_dir"
 
+export CC=${WASI_SDK_PREFIX}/bin/clang
+export CXX=${WASI_SDK_PREFIX}/bin/clang++
+export AR=${WASI_SDK_PREFIX}/bin/llvm-ar
+export HOST_CC=~/.mozbuild/clang/bin/clang
+export HOST_CXX=~/.mozbuild/clang/bin/clang++
+export HOST_AR=~/.mozbuild/clang/bin/llvm-ar
+
 # Build SpiderMonkey for WASI
 MOZCONFIG="${mozconfig}" \
 MOZ_FETCHES_DIR=~/.mozbuild \
-CC=~/.mozbuild/clang/bin/clang \
-CXX=~/.mozbuild/clang/bin/clang++ \
-AR=~/.mozbuild/clang/bin/llvm-ar \
   python3 "${working_dir}/gecko-dev/mach" \
   --no-interactive \
-    build
+    configure
+
+# Always use our own WASI sysroot, not the one mozbuild might have downloaded.
+rm -rf ~/.mozbuild/sysroot-wasm32-wasi
+ln -s "${WASI_SDK_PREFIX}/share/wasi-sysroot" ~/.mozbuild/sysroot-wasm32-wasi
+
+MOZCONFIG="${mozconfig}" \
+MOZ_FETCHES_DIR=~/.mozbuild \
+  python3 "${working_dir}/gecko-dev/mach" \
+  --no-interactive \
+    configure
+
+cd "$objdir"
+# Before actually building, we need to overwrite the .cargo/config file that mozbuild created,
+# because otherwise we can't build the Rust stdlib with -fPIC.
+# That file is created during the `pre-export` build step, so we run that now, then overwrite
+# the file, then build.
+make pre-export
+
+if [[ -f .cargo/config ]]; then
+  echo "" > .cargo/config
+fi
+
+make -j$(nproc) -s
 
 # Copy header, object, and static lib files
+cd ..
 rm -rf "$outdir"
 mkdir -p "$outdir/lib"
 
@@ -126,4 +177,8 @@ while read -r file; do
   cp "$file" "../$outdir/lib"
 done < "$script_dir/object-files.list"
 
-cp js/src/build/libjs_static.a "wasm32-wasi/${mode}/libjsrust.a" "../$outdir/lib"
+cp js/src/build/libjs_static.a "../$outdir/lib"
+
+if [[ -f "wasm32-wasi/${mode}/libjsrust.a" ]]; then
+cp "wasm32-wasi/${mode}/libjsrust.a" "../$outdir/lib"
+fi
diff --git a/gecko-revision b/gecko-revision
index c0c1b00..86ad283 100644
--- a/gecko-revision
+++ b/gecko-revision
@@ -1 +1 @@
-f9cccc2d2b173c1164f603135894affef4ed43fe
+0153ea840aeddb4382ad4decca96a9a30edf1179
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index d3704db..80c28b7 100644
--- a/rust-toolchain.toml
+++ b/rust-toolchain.toml
@@ -1,4 +1,4 @@
 [toolchain]
-channel = "1.68.2"
+channel = "nightly"
 targets = [ "wasm32-wasi" ]
 profile = "minimal"
diff --git a/wasi-sdk-url b/wasi-sdk-url
new file mode 100644
index 0000000..7628214
--- /dev/null
+++ b/wasi-sdk-url
@@ -0,0 +1 @@
+https://github.com/dicej/wasi-sdk/releases/download/filesystem-fix-v3/wasi-sdk-20.25g964191c91aac-$OS_NAME.tar.gz