turn on Firefox OffscreenCanvas support in CircleCI

OffscreenCanvas is behind the gfx.offscreencanvas.enabled
preference. The relevant tests are silently reported as ok if the
feature is not enabled. Unfortunately, these tests are still skipped
because of several bugs.

Author: hujiajie

.circleci/config.yml

@@ -62,7 +62,10 @@ jobs:
           EMCC_CORES=4 python3 emscripten/embuilder.py build ALL
           python3 emscripten/tests/runner.py test_hello_world
           mkdir tmp-firefox-profile/
-          echo 'user_pref("javascript.options.shared_memory", true);' >> tmp-firefox-profile/user.js
+          cat > tmp-firefox-profile/user.js <<EOF
+          user_pref("gfx.offscreencanvas.enabled", true);
+          user_pref("javascript.options.shared_memory", true);
+          EOF
 
           # Set up X and Openbox config (if we move to a headless browser, this may not be needed).
           mkdir -p .config/X11
@@ -143,7 +146,11 @@ jobs:
       # initial position of the mouse pointer relative to the canvas.
       # browser.test_html5_webgl_create_context is skipped because
       # anti-aliasing is not well supported.
-      - TEST_TARGET=browser skip:browser.test_sdl_ttf_render_text_solid skip:browser.test_sdl2_mouse skip:browser.test_html5_webgl_create_context
+      # browser.test_webgl_offscreen_canvas_in_pthread and
+      # browser.test_webgl_offscreen_canvas_in_mainthread_after_pthread
+      # are crashing Firefox (bugzil.la/1281796). The former case is
+      # further blocked by issue #6897.
+      - TEST_TARGET=browser skip:browser.test_sdl_ttf_render_text_solid skip:browser.test_sdl2_mouse skip:browser.test_html5_webgl_create_context skip:browser.test_webgl_offscreen_canvas_in_pthread skip:browser.test_webgl_offscreen_canvas_in_mainthread_after_pthread
       # TODO: use Firefox headless mode when https://bugzil.la/1375585 resolves
       - TEST_DEPENDENCY=dbus-x11 firefox menu openbox xinit xserver-xorg xserver-xorg-video-dummy
       - EMSCRIPTEN_BROWSER=firefox -profile tmp-firefox-profile/