--- a/toolkit/components/lz4/tests/xpcshell/data/worker_lz4.js
+++ b/toolkit/components/lz4/tests/xpcshell/data/worker_lz4.js
@@ -68,17 +68,17 @@ function test_reference_file() {
   let path = OS.Path.join("data", "compression.lz");
   let data = OS.File.read(path);
   let decompressed = Lz4.decompressFileContent(data);
   let text = (new TextDecoder()).decode(decompressed);
   do_check_eq(text, "Hello, lz4");
 }
 
 function compare_arrays(a, b) {
-  return Array.prototype.join.call(a) == Array.prototype.join.call(a);
+  return Array.prototype.join.call(a) == Array.prototype.join.call(b);
 }
 
 function run_rawcompression(name, array) {
   do_print("Raw compression test " + name);
   let length = array.byteLength;
   let compressedArray = new Uint8Array(Internals.maxCompressedSize(length));
   let compressedBytes = Internals.compress(array, length, compressedArray);
   compressedArray = new Uint8Array(compressedArray.buffer, 0, compressedBytes);

--- a/toolkit/components/lz4/tests/xpcshell/test_lz4_sync.js
+++ b/toolkit/components/lz4/tests/xpcshell/test_lz4_sync.js
@@ -1,17 +1,17 @@
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 
 const Cu = Components.utils;
 Cu.import("resource://gre/modules/lz4.js");
 Cu.import("resource://gre/modules/osfile.jsm");
 
 function compare_arrays(a, b) {
-  return Array.prototype.join.call(a) == Array.prototype.join.call(a);
+  return Array.prototype.join.call(a) == Array.prototype.join.call(b);
 }
 
 add_task(async function() {
   let path = OS.Path.join("data", "compression.lz");
   let data = await OS.File.read(path);
   let decompressed = Lz4.decompressFileContent(data);
   let text = (new TextDecoder()).decode(decompressed);
   do_check_eq(text, "Hello, lz4");