Use base browsers variable in Firestore karma config (#8876)

Author: dlarocque

packages/firestore/karma.conf.js

@@ -21,7 +21,6 @@ const { argv } = require('yargs');
 module.exports = function (config) {
   const karmaConfig = {
     ...karmaBase,
-    browsers: getTestBrowsers(argv),
     // files to load into karma
     files: getTestFiles(argv),
 
@@ -76,12 +75,4 @@ function getTestFiles(argv) {
   }
 }
 
-function getTestBrowsers(argv) {
-  let browsers = ['ChromeHeadless'];
-  if (process.env?.BROWSERS && argv.unit) {
-    browsers = process.env?.BROWSERS?.split(',');
-  }
-  return browsers;
-}
-
 module.exports.files = getTestFiles(argv);

packages/firestore/test/unit/util/bundle.test.ts

@@ -239,9 +239,21 @@ function genericBundleReadingTests(bytesPerRead: number): void {
         'Reached the end of bundle when a length string is expected.'
       );
 
-      await expect(
-        generateBundleAndParse('{metadata: "no length prefix"}', bytesPerRead)
-      ).to.be.rejectedWith(/(Unexpected end of )(?=.*JSON\b).*/gi);
+      // The multiple "rejectedWith" checks below are an attempt to make the
+      // test robust in the presence of various permutations of the error
+      // message, which is produced by the JavaScript runtime.
+      // Chrome produces: Unexpected end of JSON input
+      // Webkit produces: JSON Parse error: Unexpected EOF
+      const noLengthPrefixPromise = generateBundleAndParse(
+        '{metadata: "no length prefix"}',
+        bytesPerRead
+      );
+      await expect(noLengthPrefixPromise).to.be.rejectedWith(
+        /(\b|^)unexpected ((end of)|(eof))(\b|$)/gi
+      );
+      await expect(noLengthPrefixPromise).to.be.rejectedWith(
+        /(\b|^)JSON(\b|$)/g
+      );
 
       await expect(
         generateBundleAndParse(