diff --git a/1.3-Implementation.md b/1.3-Implementation.md
index 5a7f78c..21e6531 100644
--- a/1.3-Implementation.md
+++ b/1.3-Implementation.md
@@ -1,5 +1,5 @@
 The `thunderbird user.js` is based on the [`arkenfox user.js`](https://github.com/arkenfox/user.js) for Firefox.
 
-Each version major version of Thunderbird is based on the new ESR of Firefox. Where appropriate I have checked the options to see that they correlate to functionality within Thunderbird. This is done by manually checking [the source in dxr](https://dxr.mozilla.org/comm-release/source). If functionality does not exist the options are stripped from the config.
+Each version major version of Thunderbird is based on the new ESR of Firefox. Where appropriate I have checked the options to see that they correlate to functionality within Thunderbird. This is done by manually checking [the source on SearchFox](https://searchfox.org/comm-central/source/). If functionality does not exist the options are stripped from the config.
 
 For more general information on implementation consider reading [1.3-Implementation](https://github.com/arkenfox/user.js/wiki/1.3-Implementation) from the [arkenfox user.js](https://github.com/arkenfox/user.js) project.