diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 78ac846..9ea01db 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -30,13 +30,17 @@ jobs:
       - uses: astral-sh/setup-uv@v6
       - name: Build
         run: sh packaging/build.sh
-      - name: Libraries Firefox needs (for the smoke test)
-        if: runner.os == 'Linux'
-        run: sudo packaging/build/venv/bin/python -m playwright install-deps firefox
       - name: Smoke test
+        # Linux: first without installing Firefox's system libraries (GitHub's runners ship Firefox, so they have them;
+        # apt can take 20+ minutes when Ubuntu's mirror is slow); if it fails, they are installed and it runs once more
         run: |
           if [ "$RUNNER_OS" = Linux ]; then APP="$(ls dist/*.AppImage)"; else APP=packaging/build/dist/NUauto.app/Contents/MacOS/NUauto; fi
-          packaging/build/venv/bin/python packaging/smoke.py "$APP"
+          if ! packaging/build/venv/bin/python packaging/smoke.py "$APP"; then
+            [ "$RUNNER_OS" = Linux ] || exit 1
+            echo "Smoke test failed: installing the system libraries Firefox needs, then once more"
+            sudo packaging/build/venv/bin/python -m playwright install-deps firefox
+            packaging/build/venv/bin/python packaging/smoke.py "$APP"
+          fi
       - uses: actions/upload-artifact@v4
         with:
           name: nuauto-${{ matrix.os }}
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index a79cf09..2f4a984 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -29,6 +29,18 @@ jobs:
           uv venv --python 3.12 .venv
           uv pip install --python .venv/bin/python -e .
       - name: Install Playwright's Firefox
-        run: .venv/bin/python -m playwright install --with-deps firefox
+        # GitHub's Linux runners ship Firefox, so they already have the system libraries it needs; they are installed
+        # (apt, which can take 20+ minutes when Ubuntu's mirror is slow) only if Firefox does not start without them
+        run: |
+          .venv/bin/python -m playwright install firefox
+          if [ "$RUNNER_OS" = Linux ] && ! .venv/bin/python - <<'EOF'
+          from playwright.sync_api import sync_playwright
+          with sync_playwright() as p:
+              p.firefox.launch().close()
+          EOF
+          then
+            echo "Firefox did not start: installing the system libraries it needs"
+            sudo .venv/bin/python -m playwright install-deps firefox
+          fi
       - name: Tests
         run: .venv/bin/nuauto test
diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index 0d833a2..e49f151 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -196,7 +196,8 @@ REPO LAYOUT (what is not a module)
   deploy/systemd/ (homelab units: daily, weekly, intern, deploy, assist timers + services; web service)
   packaging/ (the packaged app: nuauto.spec, build.sh, distros.sh, entry.py, AppRun, desktop file, icons, smoke.py)
   .github/workflows/ (tests.yml: `nuauto test` on Ubuntu + macOS, on PRs and main; release.yml: AppImages + DMGs, built on
-  PRs (Intel Mac: tags only), released on v* tags)
+  PRs (Intel Mac: tags only), released on v* tags. Firefox's system libraries are installed on Linux only when Firefox
+  won't start without them: GitHub's runners already have them, and apt can take 20+ minutes on a slow Ubuntu mirror)
 
 TESTS (`nuauto test` runs every tests/test_*.py, 4 at a time: offline, no sheet, no real NUworks, no network; browser tests
 use headless Firefox on local pages or demo mode. Run it before pushing; CI runs it on Ubuntu and macOS.)