The prebuilt files include `web/pdf_viewer.js` with some viewer APIs. Those are missing from type declarations.
),
        createScriptingBundle(defines).pipe(
          gulp.dest(MOZCENTRAL_CONTENT_DIR + "build")
        ),
        createSandboxExternal(defines).pipe(
          gulp.dest(MOZCENTRAL_CONTENT_DIR + "build")
        ),
        createWorkerBundle(defines).pipe(
          gulp.dest(MOZCENTRAL_CONTENT_DIR + "build")
        ),
        createWebBundle(defines, { defaultPreferencesDir: "mozcentral/" }).pipe(
          gulp.dest(MOZCENTRAL_CONTENT_DIR + "web")
        ),
        gulp
          .src(MOZCENTRAL_COMMON_WEB_FILES, { base: "web/" })
          .pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR + "web")),
        createCMapBundle().pipe(
          gulp.dest(MOZCENTRAL_CONTENT_DIR + "web/cmaps")
        ),
        createStandardFontBundle().pipe(
          gulp.dest(MOZCENTRAL_CONTENT_DIR + "web/standard_fonts")
        ),
        preprocessHTML("web/viewer.html", defines).pipe(
          gulp.dest(MOZCENTRAL_CONTENT_DIR + "web")
        ),
        preprocessCSS("web/viewer.css", "mozcentral", defines, true)
          .pipe(
            postcss([
              autoprefixer({
                overrideBrowserslist: ["last 1 firefox versions"],