diff --git a/fetch/content-length/api-and-duplicate-headers.any.js b/fetch/content-length/api-and-duplicate-headers.any.js
new file mode 100644
index 00000000000000..8015289f8d661c
--- /dev/null
+++ b/fetch/content-length/api-and-duplicate-headers.any.js
@@ -0,0 +1,23 @@
+promise_test(async t => {
+  const response = await fetch("resources/identical-duplicates.asis");
+  assert_equals(response.statusText, "BLAH");
+  assert_equals(response.headers.get("test"), "x, x");
+  assert_equals(response.headers.get("content-type"), "text/plain, text/plain");
+  assert_equals(response.headers.get("content-length"), "6, 6");
+  const text = await response.text();
+  assert_equals(text, "Test.\n");
+}, "fetch() and duplicate Content-Length/Content-Type headers");
+
+async_test(t => {
+  const xhr = new XMLHttpRequest();
+  xhr.open("GET", "resources/identical-duplicates.asis");
+  xhr.send();
+  xhr.onload = t.step_func_done(() => {
+    assert_equals(xhr.statusText, "BLAH");
+    assert_equals(xhr.getResponseHeader("test"), "x, x");
+    assert_equals(xhr.getResponseHeader("content-type"), "text/plain, text/plain");
+    assert_equals(xhr.getResponseHeader("content-length"), "6, 6");
+    assert_equals(xhr.getAllResponseHeaders(), "content-length: 6, 6\r\ncontent-type: text/plain, text/plain\r\ntest: x, x\r\n");
+    assert_equals(xhr.responseText, "Test.\n");
+  });
+}, "XMLHttpRequest and duplicate Content-Length/Content-Type headers");
diff --git a/fetch/content-length/resources/identical-duplicates.asis b/fetch/content-length/resources/identical-duplicates.asis
new file mode 100644
index 00000000000000..f38c9a4b8a05ae
--- /dev/null
+++ b/fetch/content-length/resources/identical-duplicates.asis
@@ -0,0 +1,9 @@
+HTTP/1.1 200 BLAH
+Test: x
+Test: x
+Content-Type: text/plain
+Content-Type: text/plain
+Content-Length: 6
+Content-Length: 6
+
+Test.
diff --git a/service-workers/service-worker/resources/xhr-content-length-worker.js b/service-workers/service-worker/resources/xhr-content-length-worker.js
new file mode 100644
index 00000000000000..604deece2d252d
--- /dev/null
+++ b/service-workers/service-worker/resources/xhr-content-length-worker.js
@@ -0,0 +1,22 @@
+// Service worker for the xhr-content-length test.
+
+self.addEventListener("fetch", event => {
+  const url = new URL(event.request.url);
+  const type = url.searchParams.get("type");
+
+  if (type === "no-content-length") {
+    event.respondWith(new Response("Hello!"));
+  }
+
+  if (type === "larger-content-length") {
+    event.respondWith(new Response("meeeeh", { headers: [["Content-Length", "10000"]] }));
+  }
+
+  if (type === "double-content-length") {
+    event.respondWith(new Response("meeeeh", { headers: [["Content-Length", "10000"], ["Content-Length", "10000"]] }));
+  }
+
+  if (type === "bogus-content-length") {
+    event.respondWith(new Response("meeeeh", { headers: [["Content-Length", "test"]] }));
+  }
+});
diff --git a/service-workers/service-worker/xhr-content-length.window.js b/service-workers/service-worker/xhr-content-length.window.js
new file mode 100644
index 00000000000000..1ae320e9c3c571
--- /dev/null
+++ b/service-workers/service-worker/xhr-content-length.window.js
@@ -0,0 +1,55 @@
+// META: script=resources/test-helpers.sub.js
+
+let frame;
+
+promise_test(async (t) => {
+  const scope = "resources/empty.html";
+  const script = "resources/xhr-content-length-worker.js";
+  const registration = await service_worker_unregister_and_register(t, script, scope);
+  await wait_for_state(t, registration.installing, "activated");
+  frame = await with_iframe(scope);
+}, "Setup");
+
+promise_test(async t => {
+  const xhr = new frame.contentWindow.XMLHttpRequest();
+  xhr.open("GET", "test?type=no-content-length");
+  xhr.send();
+  const event = await new Promise(resolve => xhr.onload = resolve);
+  assert_equals(xhr.getResponseHeader("content-length"), null);
+  assert_false(event.lengthComputable);
+  assert_equals(event.total, 0);
+  assert_equals(event.loaded, xhr.responseText.length);
+}, `Synthetic response without Content-Length header`);
+
+promise_test(async t => {
+  const xhr = new frame.contentWindow.XMLHttpRequest();
+  xhr.open("GET", "test?type=larger-content-length");
+  xhr.send();
+  const event = await new Promise(resolve => xhr.onload = resolve);
+  assert_equals(xhr.getResponseHeader("content-length"), "10000");
+  assert_true(event.lengthComputable);
+  assert_equals(event.total, 10000);
+  assert_equals(event.loaded, xhr.responseText.length);
+}, `Synthetic response with Content-Length header with value larger than response body length`);
+
+promise_test(async t => {
+  const xhr = new frame.contentWindow.XMLHttpRequest();
+  xhr.open("GET", "test?type=double-content-length");
+  xhr.send();
+  const event = await new Promise(resolve => xhr.onload = resolve);
+  assert_equals(xhr.getResponseHeader("content-length"), "10000, 10000");
+  assert_true(event.lengthComputable);
+  assert_equals(event.total, 10000);
+  assert_equals(event.loaded, xhr.responseText.length);
+}, `Synthetic response with two Content-Length headers value larger than response body length`);
+
+promise_test(async t => {
+  const xhr = new frame.contentWindow.XMLHttpRequest();
+  xhr.open("GET", "test?type=bogus-content-length");
+  xhr.send();
+  const event = await new Promise(resolve => xhr.onload = resolve);
+  assert_equals(xhr.getResponseHeader("content-length"), "test");
+  assert_false(event.lengthComputable);
+  assert_equals(event.total, 0);
+  assert_equals(event.loaded, xhr.responseText.length);
+}, `Synthetic response with bogus Content-Length header`);
diff --git a/xhr/event-upload-progress.any.js b/xhr/event-upload-progress.any.js
index 87223c172d50bb..6fe659193b58fc 100644
--- a/xhr/event-upload-progress.any.js
+++ b/xhr/event-upload-progress.any.js
@@ -7,10 +7,14 @@ const remote = get_host_info().HTTP_REMOTE_ORIGIN + "/xhr/resources/corsenabled.
 [remote, redirect].forEach(url => {
   async_test(test => {
     const client = new XMLHttpRequest();
-    client.upload.onprogress = test.step_func_done();
+    const data = "On time: " + url;
+    client.upload.onprogress = test.step_func_done(e => {
+      assert_true(e.lengthComputable);
+      assert_equals(e.total, data.length);
+    });
     client.onload = test.unreached_func();
     client.open("POST", url);
-    client.send("On time: " + url);
+    client.send(data);
   }, "Upload events registered on time (" + url + ")");
 });
 
diff --git a/xhr/request-content-length.any.js b/xhr/request-content-length.any.js
new file mode 100644
index 00000000000000..054d2cce9d27ab
--- /dev/null
+++ b/xhr/request-content-length.any.js
@@ -0,0 +1,31 @@
+async_test(test => {
+  const client = new XMLHttpRequest();
+  const data = "This is 22 bytes long.";
+  let happened = false;
+  client.upload.onprogress = test.step_func(e => {
+    assert_true(e.lengthComputable);
+    assert_equals(e.total, data.length);
+    happened = true;
+  });
+  client.onload = test.step_func_done(() => {
+    assert_true(happened);
+    assert_true(client.responseText.includes(`Content-Length: ${data.length}`));
+  });
+  client.open("POST", "resources/echo-headers.py");
+  client.send(data);
+}, "Uploads need to set the Content-Length header");
+
+async_test(test => {
+  const client = new XMLHttpRequest();
+  const data = "blah";
+  const url = URL.createObjectURL(new Blob([data]));
+  client.open("GET", url);
+  client.send();
+  client.onload = test.step_func_done(e => {
+    assert_true(e.lengthComputable);
+    assert_equals(e.total, data.length);
+    assert_equals(e.loaded, data.length);
+    assert_equals(client.responseText, data);
+    assert_equals(client.getResponseHeader("Content-Length"), String(data.length));
+  });
+}, "Fetched blob: URLs set the Content-Length header");