Bug 1733845: Fix Gecko Logging doc links r=nika,sylvestre DONTBUILD

Gecko logging documentation moved earlier this year. Some docs and comments
still refer to the old URL, which now 404s.

Differential Revision: https://phabricator.services.mozilla.com/D127369

docs/testing-rust-code/index.md

@@ -102,7 +102,7 @@ To restrict logging to child processes, use `RUST_LOG_CHILD` instead of
 Rust logging can also be forwarded to the [Gecko logger] for capture via
 `MOZ_LOG` and `MOZ_LOG_FILE`.
 
-[Gecko logger]: https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Gecko_Logging
+[Gecko logger]: /xpcom/logging.html
 
 - When parsing modules from `MOZ_LOG`, modules containing `::` are considered
   to be Rust modules. To log everything in a top-level module like

dom/plugins/base/nsPluginLogging.h

@@ -37,7 +37,7 @@
 //    My favorite Win32 Example: SET MOZ_LOG_FILE=c:\temp\pluginLog.txt
 
 // 4. For complete information see the Gecko Developer guide:
-// https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Gecko_Logging
+// https://firefox-source-docs.mozilla.org/xpcom/logging.html
 
 class nsPluginLogging {
  public:

toolkit/components/telemetry/tests/marionette/harness/telemetry_harness/fog_testcase.py

@@ -46,7 +46,7 @@ def setUp(self, *args, **kwargs):
             {
                 "telemetry.fog.test.localhost_port": self.fog_ping_server.port,
                 # Enable FOG logging. 5 means "Verbose". See
-                # https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Gecko_Logging
+                # https://firefox-source-docs.mozilla.org/xpcom/logging.html
                 # for details.
                 "logging.config.clear_on_startup": False,
                 "logging.config.sync": True,