Updating.md

@@ -137,6 +137,9 @@ Setting a custom updater URL will also override the update certificate: copy you
 
 If you are testing `release` or `alpha`, you will have to modify the `build` script to replace the release key instead of the nightly.
 
+Since you are creating new builds for testing purposes, it is a good idea to add some code to help you to debug the updater binary.
+See the troubleshooting section.
+
 ## Sign MAR file
 
 ```sh
@@ -263,4 +266,39 @@ At this point, Firefox should find the update automatically, download it, and ap
 
 ### Troubleshooting
 
+#### Logs
+
 Updater logs can be enabled in the browser by setting `app.update.log` to `true`, and are visible in the JavaScript console.
+
+This helps to find deploy and/or download errors (e.g., wrong URL in the `config.yml`, unsigned mars etc...).
+
+Errors that occurred during the update process are usually logged in `UpdateInfo/updates/last-update.log`.
+
+#### Attaching a debugger
+
+The `updater` process is started by Firefox, therefore it is very difficult to start it in a debugging environment.
+
+There are a couple of workarounds that involve modify adding some code at the beginning of `NS_main` in `toolkit/mozapps/update/updater/updater.cpp`.
+
+If you are on Windows, you can add a `__debugbreak();` line, and you will be able to attach the debugger.
+However, if you can't debug it, there is no way to resume the updater.
+
+A similar approach is to add some sleep, whose value depends on an environment variable.
+For example, this will work on Windows:
+
+```c++
+  const char *shouldDelay = getenv("TBB_UPDATER_DELAY");
+  if (shouldDelay) {
+    char *endptr;
+    long d = strtol(shouldDelay, &endptr, 10);
+    if (endptr == shouldDelay) {
+      d = 60;
+    }
+    Sleep(d * 1000);
+  }
+```
+
+For other platforms, you will need to change `Sleep` with something else (maybe `std::this_thread::sleep_for` will work).
+
+At that point, you can define a number of seconds to sleep and let you attach the debugger by setting `TBB_UPDATER_DELAY` before running the Firefox process.
+Luckily, Firefox will pass the environment variables to the updater process.
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