--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -8480,16 +8480,26 @@
   "DEVTOOLS_DEBUGGER_DISPLAY_SOURCE_REMOTE_MS": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "never",
     "kind": "exponential",
     "high": 10000,
     "n_buckets": 1000,
     "description": "The time (in milliseconds) that it took to display a selected source to the user."
   },
+  "DEVTOOLS_DEBUGGER_LOAD_SOURCE_MS": {
+    "record_in_processes": ["main", "content"],
+    "alert_emails": ["dev-developer-tools@lists.mozilla.org", "hkirschner@mozilla.com"],
+    "bug_numbers": [1429047],
+    "expires_in_version": "66",
+    "kind": "exponential",
+    "high": 10000,
+    "n_buckets": 100,
+    "description": "The time (in milliseconds) that it took to load a source for the user."
+  },
   "DEVTOOLS_ABOUT_DEVTOOLS_OPENED_KEY": {
     "record_in_processes": ["main"],
     "alert_emails": ["dev-developer-tools@lists.mozilla.org", "hkirschner@mozilla.com"],
     "bug_numbers": [1412029],
     "expires_in_version": "63",
     "kind": "categorical",
     "labels": ["toggleToolbox", "toggleToolboxF12", "inspector", "webconsole", "jsdebugger", "netmonitor", "toggleToolbar", "webide", "browserToolbox", "browserConsole", "responsiveDesignMode", "scratchpad", "styleeditor", "performance", "storage", "dom"],
     "description": "Records the key shortcut passed to open the about:devtools page."