--- a/dom/base/test/browser_use_counters.js
+++ b/dom/base/test/browser_use_counters.js
@@ -106,19 +106,19 @@ function waitForPageLoad(browser) {
   });
 }
 
 function grabHistogramsFromContent(use_counter_middlefix, page_before = null) {
   let telemetry = Cc["@mozilla.org/base/telemetry;1"].getService(Ci.nsITelemetry);
   let gather = () => {
     let snapshots;
     if (Services.appinfo.browserTabsRemoteAutostart) {
-      snapshots = telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN, false, false).content;
+      snapshots = telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN, false).content;
     } else {
-      snapshots = telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN, false, false).parent;
+      snapshots = telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN, false).parent;
     }
     let checkGet = (probe) => {
       return snapshots[probe] ? snapshots[probe].sum : 0;
     };
     return [
       checkGet("USE_COUNTER2_" + use_counter_middlefix + "_PAGE"),
       checkGet("USE_COUNTER2_" + use_counter_middlefix + "_DOCUMENT"),
       checkGet("CONTENT_DOCUMENTS_DESTROYED"),

--- a/toolkit/components/extensions/test/xpcshell/head_telemetry.js
+++ b/toolkit/components/extensions/test/xpcshell/head_telemetry.js
@@ -10,30 +10,27 @@ ChromeUtils.defineModuleGetter(this, "Co
 const IS_OOP = Services.prefs.getBoolPref("extensions.webextensions.remote");
 
 function arraySum(arr) {
   return arr.reduce((a, b) => a + b, 0);
 }
 
 function clearHistograms() {
   Services.telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
-                                        true /* subsession */,
                                         true /* clear */);
 }
 
 function getSnapshots(process) {
   return Services.telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
-                                               true /* subsession */,
                                                false /* clear */)[process];
 }
 
 // TODO Bug 1357509: There is no good way to make sure that the parent received
 // the histogram entries from the extension and content processes.  Let's stick
 // to the ugly, spinning the event loop until we have a good approach.
 function promiseTelemetryRecorded(id, process, expectedCount) {
   let condition = () => {
     let snapshot = Services.telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
-                                                         true /* subsession */,
                                                          false /* clear */)[process][id];
     return snapshot && arraySum(snapshot.counts) >= expectedCount;
   };
   return ContentTaskUtils.waitForCondition(condition);
 }

--- a/toolkit/components/osfile/tests/xpcshell/test_telemetry.js
+++ b/toolkit/components/osfile/tests/xpcshell/test_telemetry.js
@@ -23,45 +23,41 @@ function getCount(histogram) {
 
 // Ensure that launching the OS.File worker adds data to the relevant
 // histograms
 add_task(async function test_startup() {
   let LAUNCH = "OSFILE_WORKER_LAUNCH_MS";
   let READY = "OSFILE_WORKER_READY_MS";
 
   let before = Services.telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
-                                                     false,
                                                      false).parent;
 
   // Launch the OS.File worker
   await File.getCurrentDirectory();
 
   let after = Services.telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
-                                                    false,
                                                     false).parent;
 
 
   info("Ensuring that we have recorded measures for histograms");
   Assert.equal(getCount(after[LAUNCH]), getCount(before[LAUNCH]) + 1);
   Assert.equal(getCount(after[READY]), getCount(before[READY]) + 1);
 
   info("Ensuring that launh <= ready");
   Assert.ok(after[LAUNCH].sum <= after[READY].sum);
 });
 
 // Ensure that calling writeAtomic adds data to the relevant histograms
 add_task(async function test_writeAtomic() {
   let LABEL = "OSFILE_WRITEATOMIC_JANK_MS";
 
   let before = Services.telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
-                                                     false,
                                                      false).parent;
 
   // Perform a write.
   let path = Path.join(Constants.Path.profileDir, "test_osfile_telemetry.tmp");
   await File.writeAtomic(path, LABEL, { tmpPath: path + ".tmp" } );
 
   let after = Services.telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
-                                                    false,
                                                     false).parent;
 
   Assert.equal(getCount(after[LABEL]), getCount(before[LABEL]) + 1);
 });

--- a/toolkit/components/terminator/tests/xpcshell/test_terminator_reload.js
+++ b/toolkit/components/terminator/tests/xpcshell/test_terminator_reload.js
@@ -25,17 +25,16 @@ add_task(async function init() {
   do_get_profile();
   PATH = Path.join(Constants.Path.localProfileDir, "ShutdownDuration.json");
 });
 
 add_task(async function test_reload() {
   info("Forging data");
   let data = {};
   let telemetrySnapshots = Services.telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
-                                                                 false /* subsession */,
                                                                  false /* clear */).parent;
   let i = 0;
   for (let k of Object.keys(HISTOGRAMS)) {
     let id = HISTOGRAMS[k];
     data[k] = i++;
     Assert.equal(telemetrySnapshots[id] || undefined, undefined, "Histogram " + id + " is empty");
   }
 
@@ -58,17 +57,16 @@ add_task(async function test_reload() {
     createInstance(Ci.nsIObserver);
   tt.observe(null, "profile-after-change", "");
 
   info("Waiting until telemetry is updated");
   // Now wait until Telemetry is updated
   await wait;
 
   telemetrySnapshots = Services.telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
-                                                             false /* subsession */,
                                                              false /* clear */).parent;
   for (let k of Object.keys(HISTOGRAMS)) {
     let id = HISTOGRAMS[k];
     info("Testing histogram " + id);
     let snapshot = telemetrySnapshots[id];
     let count = 0;
     for (let x of snapshot.counts) {
       count += x;