Switch e2e screenshot browser to firefox-esr (#881)

Chrome 147+ fails to produce --headless --screenshot images in the
e2e container (Page.captureScreenshot regression), which made the
e2e-test job exhaust its 30-min polling window and fail. Replace
google-chrome-stable with firefox-esr from the Mozilla Team PPA
(base image is Ubuntu 24.04 Noble). The shared browser-helpers.sh
in ghcr.io/guysoft/custompios:devel now prefers firefox-esr/firefox
and falls back to Chrome, so this pairs with the CustomPiOS helper
update. Validated locally: firefox-esr 140.13.0esr installs and
--headless --no-remote --screenshot emits a real PNG.

Author: guysoft

testing/Dockerfile

@@ -6,11 +6,11 @@ FROM ptrsr/pi-ci:latest
 ENV LIBGUESTFS_BACKEND=direct
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
-    sshpass openssh-client curl socat imagemagick wget gnupg \
-    dbus dbus-x11 fonts-liberation tesseract-ocr \
-    && wget -q -O - https://dl.google.com/linux/linux_signing_key.pub | gpg --dearmor -o /usr/share/keyrings/google-chrome.gpg \
-    && echo "deb [arch=amd64 signed-by=/usr/share/keyrings/google-chrome.gpg] http://dl.google.com/linux/chrome/deb/ stable main" > /etc/apt/sources.list.d/google-chrome.list \
-    && apt-get update && apt-get install -y --no-install-recommends google-chrome-stable \
+    sshpass openssh-client curl socat imagemagick wget gnupg ca-certificates \
+    dbus dbus-x11 fonts-liberation fonts-noto-cjk tesseract-ocr \
+    software-properties-common \
+    && add-apt-repository -y ppa:mozillateam/ppa \
+    && apt-get update && apt-get install -y --no-install-recommends firefox-esr \
     && rm -rf /var/lib/apt/lists/*
 
 COPY --from=custompios /CustomPiOS/distro_testing/scripts/ /test/scripts/