--- a/browser/components/downloads/DownloadsCommon.jsm
+++ b/browser/components/downloads/DownloadsCommon.jsm
@@ -75,150 +75,22 @@ const kDownloadsStringsRequiringFormatti
 const kDownloadsStringsRequiringPluralForm = {
   otherDownloads3: true,
 };
 
 const kMaxHistoryResultsForLimitedView = 42;
 
 const kPrefBranch = Services.prefs.getBranch("browser.download.");
 
-const kFileExtensions = [
-  "aac",
-  "adt",
-  "adts",
-  "accdb",
-  "accde",
-  "accdr",
-  "accdt",
-  "aif",
-  "aifc",
-  "aiff",
-  "apng",
-  "aspx",
-  "avi",
-  "avif",
-  "bat",
-  "bin",
-  "bmp",
-  "cab",
-  "cda",
-  "csv",
-  "dif",
-  "dll",
-  "doc",
-  "docm",
-  "docx",
-  "dot",
-  "dotx",
-  "eml",
-  "eps",
-  "exe",
-  "flac",
-  "flv",
-  "gif",
-  "htm",
-  "html",
-  "ico",
-  "ini",
-  "iso",
-  "jar",
-  "jfif",
-  "jpg",
-  "jpeg",
-  "json",
-  "m4a",
-  "mdb",
-  "mid",
-  "midi",
-  "mov",
-  "mp3",
-  "mp4",
-  "mpeg",
-  "mpg",
-  "msi",
-  "mui",
-  "oga",
-  "ogg",
-  "ogv",
-  "opus",
-  "pdf",
-  "pjpeg",
-  "pjp",
-  "png",
-  "pot",
-  "potm",
-  "potx",
-  "ppam",
-  "pps",
-  "ppsm",
-  "ppsx",
-  "ppt",
-  "pptm",
-  "pptx",
-  "psd",
-  "pst",
-  "pub",
-  "rar",
-  "rdf",
-  "rtf",
-  "shtml",
-  "sldm",
-  "sldx",
-  "svg",
-  "swf",
-  "sys",
-  "tif",
-  "tiff",
-  "tmp",
-  "txt",
-  "vob",
-  "vsd",
-  "vsdm",
-  "vsdx",
-  "vss",
-  "vssm",
-  "vst",
-  "vstm",
-  "vstx",
-  "wav",
-  "wbk",
-  "webm",
-  "webp",
-  "wks",
-  "wma",
-  "wmd",
-  "wmv",
-  "wmz",
-  "wms",
-  "wpd",
-  "wp5",
-  "xht",
-  "xhtml",
-  "xla",
-  "xlam",
-  "xll",
-  "xlm",
-  "xls",
-  "xlsm",
-  "xlsx",
-  "xlt",
-  "xltm",
-  "xltx",
-  "xml",
-  "zip",
-];
-
 const kGenericContentTypes = [
   "application/octet-stream",
   "binary/octet-stream",
   "application/unknown",
 ];
 
-const TELEMETRY_EVENT_CATEGORY = "downloads";
-
 var PrefObserver = {
   QueryInterface: ChromeUtils.generateQI([
     "nsIObserver",
     "nsISupportsWeakReference",
   ]),
   getPref(name) {
     try {
       switch (typeof this.prefs[name]) {
@@ -948,36 +820,16 @@ DownloadsDataCtor.prototype = {
       ? PrivateDownloadsIndicatorData
       : DownloadsIndicatorData;
     indicatorData.attention = DownloadsCommon.ATTENTION_NONE;
   },
 
   // Integration with the asynchronous Downloads back-end
 
   onDownloadAdded(download) {
-    let extension = download.target.path.split(".").pop();
-
-    if (!kFileExtensions.includes(extension)) {
-      extension = "other";
-    }
-
-    try {
-      Services.telemetry.recordEvent(
-        TELEMETRY_EVENT_CATEGORY,
-        "added",
-        "fileExtension",
-        extension,
-        {}
-      );
-    } catch (ex) {
-      Cu.reportError(
-        "DownloadsCommon: error recording telemetry event. " + ex.message
-      );
-    }
-
     // Download objects do not store the end time of downloads, as the Downloads
     // API does not need to persist this information for all platforms. Once a
     // download terminates on a Desktop browser, it becomes a history download,
     // for which the end time is stored differently, as a Places annotation.
     download.endTime = Date.now();
 
     this.oldDownloadStates.set(
       download,

--- a/toolkit/components/downloads/DownloadList.jsm
+++ b/toolkit/components/downloads/DownloadList.jsm
@@ -9,16 +9,146 @@
 "use strict";
 
 var EXPORTED_SYMBOLS = [
   "DownloadList",
   "DownloadCombinedList",
   "DownloadSummary",
 ];
 
+const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
+
+const kFileExtensions = [
+  "aac",
+  "adt",
+  "adts",
+  "accdb",
+  "accde",
+  "accdr",
+  "accdt",
+  "aif",
+  "aifc",
+  "aiff",
+  "apng",
+  "aspx",
+  "avi",
+  "avif",
+  "bat",
+  "bin",
+  "bmp",
+  "cab",
+  "cda",
+  "csv",
+  "dif",
+  "dll",
+  "doc",
+  "docm",
+  "docx",
+  "dot",
+  "dotx",
+  "eml",
+  "eps",
+  "exe",
+  "flac",
+  "flv",
+  "gif",
+  "htm",
+  "html",
+  "ico",
+  "ini",
+  "iso",
+  "jar",
+  "jfif",
+  "jpg",
+  "jpeg",
+  "json",
+  "m4a",
+  "mdb",
+  "mid",
+  "midi",
+  "mov",
+  "mp3",
+  "mp4",
+  "mpeg",
+  "mpg",
+  "msi",
+  "mui",
+  "oga",
+  "ogg",
+  "ogv",
+  "opus",
+  "pdf",
+  "pjpeg",
+  "pjp",
+  "png",
+  "pot",
+  "potm",
+  "potx",
+  "ppam",
+  "pps",
+  "ppsm",
+  "ppsx",
+  "ppt",
+  "pptm",
+  "pptx",
+  "psd",
+  "pst",
+  "pub",
+  "rar",
+  "rdf",
+  "rtf",
+  "shtml",
+  "sldm",
+  "sldx",
+  "svg",
+  "swf",
+  "sys",
+  "tif",
+  "tiff",
+  "tmp",
+  "txt",
+  "vob",
+  "vsd",
+  "vsdm",
+  "vsdx",
+  "vss",
+  "vssm",
+  "vst",
+  "vstm",
+  "vstx",
+  "wav",
+  "wbk",
+  "webm",
+  "webp",
+  "wks",
+  "wma",
+  "wmd",
+  "wmv",
+  "wmz",
+  "wms",
+  "wpd",
+  "wp5",
+  "xht",
+  "xhtml",
+  "xla",
+  "xlam",
+  "xll",
+  "xlm",
+  "xls",
+  "xlsm",
+  "xlsx",
+  "xlt",
+  "xltm",
+  "xltx",
+  "xml",
+  "zip",
+];
+
+const TELEMETRY_EVENT_CATEGORY = "downloads";
+
 /**
  * Represents a collection of Download objects that can be viewed and managed by
  * the user interface, and persisted across sessions.
  */
 var DownloadList = function() {
   this._downloads = [];
   this._views = new Set();
 };
@@ -289,16 +419,36 @@ DownloadCombinedList.prototype = {
    * @param aDownload
    *        The Download object to add.
    *
    * @return {Promise}
    * @resolves When the download has been added.
    * @rejects JavaScript exception.
    */
   add(aDownload) {
+    let extension = aDownload.target.path.split(".").pop();
+
+    if (!kFileExtensions.includes(extension)) {
+      extension = "other";
+    }
+
+    try {
+      Services.telemetry.recordEvent(
+        TELEMETRY_EVENT_CATEGORY,
+        "added",
+        "fileExtension",
+        extension,
+        {}
+      );
+    } catch (ex) {
+      Cu.reportError(
+        "DownloadsCommon: error recording telemetry event. " + ex.message
+      );
+    }
+
     if (aDownload.source.isPrivate) {
       return this._privateList.add(aDownload);
     }
     return this._publicList.add(aDownload);
   },
 
   /**
    * Removes a download from the list.  If the download was already removed,

--- a/toolkit/components/telemetry/Events.yaml
+++ b/toolkit/components/telemetry/Events.yaml
@@ -422,20 +422,20 @@ blocklist:
       - "firefox"
     record_in_processes: ["main"]
     bug_numbers: [1662857]
     release_channel_collection: opt-out
 
 downloads:
   added:
     description: >
-      Sent when downloading a new file. Possible values are in contained in DownloadsCommon::kFileExtensions.
+      Sent when downloading a new file. Possible values are in contained in DownloadList::kFileExtensions.
       All other downloads not in the listare marked as other.
     objects: ["fileExtension"]
-    bug_numbers: [1627676]
+    bug_numbers: [1627676, 1706355]
     notification_emails: ["rtestard@mozilla.com", "emalysz@mozilla.com"]
     products:
       - "firefox"
     record_in_processes: ["main"]
     release_channel_collection: opt-out
     expiry_version: never
 
 form_autocomplete: