[wasm][debugger] Use new image to run debugger tests on firefox (dotnet#68859)

* test firefox in the docker image

* remove unnecessary comments

Author: thaystg

eng/pipelines/libraries/helix-queues-setup.yml

@@ -179,7 +179,7 @@ jobs:
 
     # WebAssembly Firefox
     - ${{ if eq(parameters.platform, 'Browser_wasm_firefox') }}:
-      - (Ubuntu.1804.Amd64)Ubuntu.1804.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-18.04-webassembly-20220408155625-5bc1463
+      - (Ubuntu.1804.Amd64)Ubuntu.1804.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-18.04-helix-webassembly-20220504035734-67908a0
 
     # WebAssembly windows
     - ${{ if eq(parameters.platform, 'Browser_wasm_win') }}:

src/mono/wasm/debugger/BrowserDebugProxy/Firefox/FirefoxMonoProxy.cs

@@ -154,8 +154,6 @@ protected override Task ProcessBrowserMessage(string msg, CancellationToken toke
                     return SendCommandInternal(msgId, "", res, token);
                 return null;
             }
-            //{"type":"evaluationResult","resultID":"1634575904746-0","hasException":false,"input":"ret = 10","result":10,"startTime":1634575904746,"timestamp":1634575904748,"from":"server1.conn21.child10/consoleActor2"}
-
             return null;
         }
         catch (Exception ex)