diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index 8a2db1c516..53c3bac101 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -4846,70 +4846,6 @@
     "n_buckets": 202,
     "description": "Size (in bytes) of the compressed crash store JSON file."
   },
-  "PDF_VIEWER_USED": {
-    "expires_in_version": "default",
-    "kind": "boolean",
-    "description": "How many times PDF Viewer was used"
-  },
-  "PDF_VIEWER_FALLBACK_SHOWN": {
-    "expires_in_version": "default",
-    "kind": "boolean",
-    "description": "How many times PDF Viewer fallback bar was shown"
-  },
-  "PDF_VIEWER_PRINT": {
-    "expires_in_version": "never",
-    "kind": "boolean",
-    "description": "How many times PDF Viewer print functionality was used"
-  },
-  "PDF_VIEWER_DOCUMENT_VERSION": {
-    "expires_in_version": "default",
-    "kind": "enumerated",
-    "n_values": 20,
-    "description": "The PDF document version (1.1, 1.2, etc.)"
-  },
-  "PDF_VIEWER_DOCUMENT_GENERATOR": {
-    "expires_in_version": "default",
-    "kind": "enumerated",
-    "n_values": 30,
-    "description": "The PDF document generator"
-  },
-  "PDF_VIEWER_DOCUMENT_SIZE_KB": {
-    "expires_in_version": "default",
-    "kind": "exponential",
-    "low": "2",
-    "high": "64 * 1024",
-    "n_buckets": 20,
-    "description": "The PDF document size (KB)"
-  },
-  "PDF_VIEWER_FONT_TYPES": {
-    "expires_in_version": "never",
-    "kind": "enumerated",
-    "n_values": 19,
-    "description": "The PDF document font types used"
-  },
-  "PDF_VIEWER_EMBED": {
-    "expires_in_version": "never",
-    "kind": "boolean",
-    "description": "A PDF document was embedded: true using OBJECT/EMBED and false using IFRAME"
-  },
-  "PDF_VIEWER_FORM": {
-    "expires_in_version": "default",
-    "kind": "boolean",
-    "description": "A PDF form expected: true for AcroForm and false for XFA"
-  },
-  "PDF_VIEWER_STREAM_TYPES": {
-    "expires_in_version": "never",
-    "kind": "enumerated",
-    "n_values": 19,
-    "description": "The PDF document compression stream types used"
-  },
-  "PDF_VIEWER_TIME_TO_VIEW_MS": {
-    "expires_in_version": "default",
-    "kind": "exponential",
-    "high": "10000",
-    "n_buckets": 50,
-    "description": "Time spent to display first page in PDF Viewer (ms)"
-  },
   "SHUMWAY_TIME_TO_VIEW_MS": {
     "expires_in_version": "40",
     "kind": "exponential",