diff --git a/docs/browser-builds.md b/docs/browser-builds.md
index 7a4091e..d1cd6fb 100644
--- a/docs/browser-builds.md
+++ b/docs/browser-builds.md
@@ -52,15 +52,29 @@ Run the first desktop configure probe:
 AMPB_DESKTOP_BUILD_PROBE_MODE=configure sh tools/browser-desktop-build-probe.sh
 ```
 
+Run the first desktop source build:
+
+```sh
+AMPB_DESKTOP_BUILD_PROBE_MODE=build sh tools/browser-desktop-build-probe.sh
+```
+
+The default `source` flavor is the verified desktop path. Use
+`AMPB_DESKTOP_BUILD_FLAVOR=artifact` only as a faster optional probe; it depends on
+Mozilla artifact availability for the selected checkout.
+
 The probe writes:
 
-- `/tmp/ampb-browser-build/mozconfigs/desktop-debug.mozconfig`
-- `/tmp/ampb-browser-build/obj/gecko-desktop-debug`
-- `/tmp/ampb-browser-build/logs/gecko-desktop-mach-help.log`
-- `/tmp/ampb-browser-build/logs/gecko-desktop-mach-configure.log`
+- `/tmp/ampb-browser-build/mozconfigs/desktop-source.mozconfig`
+- `/tmp/ampb-browser-build/obj/gecko-desktop-source`
+- `/tmp/ampb-browser-build/logs/gecko-desktop-source-mach-help.log`
+- `/tmp/ampb-browser-build/logs/gecko-desktop-source-mach-configure.log`
+- `/tmp/ampb-browser-build/logs/gecko-desktop-source-mach-build.log`
 
-Configure mode may install Mozilla build Python helpers such as `zstandard` into mach
-virtualenvs under `/tmp/ampb-browser-build/cache/mozbuild`.
+A successful source build produces a bundled app at
+`/tmp/ampb-browser-build/obj/gecko-desktop-source/dist/Nightly.app`.
+
+Configure and build modes may install Mozilla build Python helpers such as `zstandard`
+into mach virtualenvs under `/tmp/ampb-browser-build/cache/mozbuild`.
 
 ## Source Plan
 
diff --git a/docs/desktop-vertical.md b/docs/desktop-vertical.md
index 8bdaa61..9bfc287 100644
--- a/docs/desktop-vertical.md
+++ b/docs/desktop-vertical.md
@@ -14,12 +14,16 @@ Use the external build workspace:
 ```sh
 sh tools/browser-build-workspace.sh
 sh tools/browser-source-sync.sh
-AMPB_DESKTOP_BUILD_PROBE_MODE=configure sh tools/browser-desktop-build-probe.sh
+AMPB_DESKTOP_BUILD_PROBE_MODE=build sh tools/browser-desktop-build-probe.sh
 ```
 
 The desktop probe keeps Gecko source, object files, downloaded toolchains, Python
 virtualenvs, pip cache, and logs under `/tmp/ampb-browser-build`.
 
+The default build flavor is the verified source build. Use
+`AMPB_DESKTOP_BUILD_FLAVOR=artifact` only as a faster optional probe when upstream
+artifacts are available for the selected checkout.
+
 ## Transport Path
 
 The first transport target is Tor through an AMPB-owned Arti/Tor runtime. The desktop
diff --git a/tools/browser-desktop-build-probe.sh b/tools/browser-desktop-build-probe.sh
index b859f2b..5a9e43f 100644
--- a/tools/browser-desktop-build-probe.sh
+++ b/tools/browser-desktop-build-probe.sh
@@ -4,9 +4,10 @@ set -eu
 root="${AMPB_BROWSER_BUILD_ROOT:-/tmp/ampb-browser-build}"
 gecko_dir="$root/src/gecko-dev"
 mode="${AMPB_DESKTOP_BUILD_PROBE_MODE:-help}"
-log="$root/logs/gecko-desktop-mach-${mode}.log"
-mozconfig="$root/mozconfigs/desktop-debug.mozconfig"
-objdir="$root/obj/gecko-desktop-debug"
+flavor="${AMPB_DESKTOP_BUILD_FLAVOR:-source}"
+log="$root/logs/gecko-desktop-${flavor}-mach-${mode}.log"
+mozconfig="$root/mozconfigs/desktop-${flavor}.mozconfig"
+objdir="$root/obj/gecko-desktop-${flavor}"
 
 if [ ! -d "$gecko_dir" ]; then
   printf 'missing gecko checkout: %s\n' "$gecko_dir" >&2
@@ -26,9 +27,17 @@ mk_add_options MOZ_OBJDIR=$objdir
 ac_add_options --enable-application=browser
 ac_add_options --disable-crashreporter
 ac_add_options --disable-debug
-ac_add_options --enable-optimize
 EOF
 
+if [ "$flavor" = "artifact" ]; then
+  printf '%s\n' 'ac_add_options --enable-artifact-builds' >>"$mozconfig"
+elif [ "$flavor" != "source" ]; then
+  printf 'unsupported AMPB_DESKTOP_BUILD_FLAVOR: %s\n' "$flavor" >&2
+  exit 2
+else
+  printf '%s\n' 'ac_add_options --enable-optimize' >>"$mozconfig"
+fi
+
 cd "$gecko_dir"
 
 mach_env() {
@@ -59,10 +68,15 @@ case "$mode" in
     ensure_zstandard
     mach_env ./mach configure >"$log" 2>&1
     ;;
+  build)
+    mach_env ./mach build --help >/dev/null 2>&1
+    ensure_zstandard
+    mach_env ./mach build >"$log" 2>&1
+    ;;
   *)
     printf 'unsupported AMPB_DESKTOP_BUILD_PROBE_MODE: %s\n' "$mode" >&2
     exit 2
     ;;
 esac
 
-printf 'AMPB_DESKTOP_BUILD_PROBE status=ok mode=%s mozconfig=%s objdir=%s log=%s\n' "$mode" "$mozconfig" "$objdir" "$log"
+printf 'AMPB_DESKTOP_BUILD_PROBE status=ok mode=%s flavor=%s mozconfig=%s objdir=%s log=%s\n' "$mode" "$flavor" "$mozconfig" "$objdir" "$log"
diff --git a/tools/browser-source-plan.sh b/tools/browser-source-plan.sh
index 7891e3b..abb0cd6 100644
--- a/tools/browser-source-plan.sh
+++ b/tools/browser-source-plan.sh
@@ -16,5 +16,5 @@ printf 'AMPB_TOR_BROWSER_BUILD_REPO=%s\n' "$tor_build_repo"
 printf 'AMPB_TOR_BROWSER_BUILD_DIR=%s\n' "$root/src/tor-browser-build"
 printf 'AMPB_GRADLE_USER_HOME=%s\n' "$root/cache/gradle"
 printf 'AMPB_MOZBUILD_STATE_PATH=%s\n' "$root/cache/mozbuild"
-printf 'AMPB_DESKTOP_BUILD_LOG=%s\n' "$root/logs/gecko-desktop-mach-help.log"
+printf 'AMPB_DESKTOP_BUILD_LOG=%s\n' "$root/logs/gecko-desktop-source-mach-build.log"
 printf 'AMPB_ANDROID_BUILD_LOG=%s\n' "$root/logs/gecko-android-mach-probe.log"