--- a/devtools/client/locales/en-US/netmonitor.properties
+++ b/devtools/client/locales/en-US/netmonitor.properties
@@ -744,8 +744,12 @@ netmonitor.custom.send=Send
 
 # LOCALIZATION NOTE (netmonitor.custom.cancel): This is the label displayed
 # on the button which cancels and closes the custom request form
 netmonitor.custom.cancel=Cancel
 
 # LOCALIZATION NOTE (netmonitor.backButton): This is the label displayed
 # on the button which exists the performance statistics view
 netmonitor.backButton=Back
+
+# LOCALIZATION NOTE (netmonitor.headers.learnMore): This is the label displayed
+# next to a header list item, with a link to external documentation
+netmonitor.headers.learnMore=Learn More

new file mode 100644
--- /dev/null
+++ b/devtools/client/netmonitor/shared/components/headers-mdn.js
@@ -0,0 +1,119 @@
+/* this source code form is subject to the terms of the mozilla public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A mapping of header names to external documentation. Any header included
+ * here will show a "Learn More" link alongside it.
+ */
+
+"use strict";
+
+var URL_DOMAIN = "https://developer.mozilla.org";
+const URL_PATH = "/en-US/docs/Web/HTTP/Headers/";
+const URL_PARAMS =
+  "?utm_source=mozilla&utm_medium=devtools-netmonitor&utm_campaign=default";
+
+var SUPPORTED_HEADERS = [
+  "Accept",
+  "Accept-Charset",
+  "Accept-Encoding",
+  "Accept-Language",
+  "Accept-Ranges",
+  "Access-Control-Allow-Credentials",
+  "Access-Control-Allow-Headers",
+  "Access-Control-Allow-Methods",
+  "Access-Control-Allow-Origin",
+  "Access-Control-Expose-Headers",
+  "Access-Control-Max-Age",
+  "Access-Control-Request-Headers",
+  "Access-Control-Request-Method",
+  "Age",
+  "Cache-Control",
+  "Connection",
+  "Content-Disposition",
+  "Content-Encoding",
+  "Content-Language",
+  "Content-Length",
+  "Content-Location",
+  "Content-Security-Policy",
+  "Content-Security-Policy-Report-Only",
+  "Content-Type",
+  "Cookie",
+  "Cookie2",
+  "DNT",
+  "Date",
+  "ETag",
+  "Expires",
+  "From",
+  "Host",
+  "If-Match",
+  "If-Modified-Since",
+  "If-None-Match",
+  "If-Range",
+  "If-Unmodified-Since",
+  "Keep-Alive",
+  "Last-Modified",
+  "Location",
+  "Origin",
+  "Pragma",
+  "Public-Key-Pins",
+  "Public-Key-Pins-Report-Only",
+  "Referer",
+  "Referrer-Policy",
+  "Retry-After",
+  "Server",
+  "Set-Cookie",
+  "Set-Cookie2",
+  "Strict-Transport-Security",
+  "TE",
+  "Tk",
+  "Trailer",
+  "Transfer-Encoding",
+  "Upgrade-Insecure-Requests",
+  "User-Agent",
+  "Vary",
+  "Via",
+  "Warning",
+  "X-Content-Type-Options",
+  "X-DNS-Prefetch-Control",
+  "X-Frame-Options",
+  "X-XSS-Protection"
+];
+
+/**
+ * Get the MDN URL for the specified header
+ *
+ * @param {string} Name of the header
+ * The baseURL to use.
+ *
+ * @return {string}
+ * The MDN URL for the header, or null if not available.
+ */
+exports.getURL = (header) => {
+  if (SUPPORTED_HEADERS.indexOf(header) === -1) {
+    return null;
+  }
+
+  return URL_DOMAIN + URL_PATH + header + URL_PARAMS;
+};
+
+/**
+ * Use a different domain for the URLs. Used only for testing.
+ *
+ * @param {string} domain
+ * The domain to use.
+ */
+exports.setDomain = (domain) => {
+  URL_DOMAIN = domain;
+};
+
+/**
+ * Use a different list of supported headers. Used only for testing.
+ *
+ * @param {array} headers
+ * The supported headers to use.
+ */
+exports.setSupportedHeaders = (headers) => {
+  SUPPORTED_HEADERS = headers;
+};

--- a/devtools/client/netmonitor/shared/components/headers-panel.js
+++ b/devtools/client/netmonitor/shared/components/headers-panel.js
@@ -10,21 +10,26 @@ const {
   createClass,
   createFactory,
   DOM,
   PropTypes,
 } = require("devtools/client/shared/vendor/react");
 const { L10N } = require("../../l10n");
 const { writeHeaderText } = require("../../request-utils");
 const { getFormattedSize } = require("../../utils/format-utils");
+const Services = require("Services");
+const { gDevTools } = require("devtools/client/framework/devtools");
+const HeadersMDN = require("devtools/client/netmonitor/shared/components/headers-mdn");
+const { REPS, MODE } = require("devtools/client/shared/components/reps/load-reps");
+const Rep = createFactory(REPS.Rep);
 
 // Components
 const PropertiesView = createFactory(require("./properties-view"));
 
-const { div, input, textarea } = DOM;
+const { a, div, input, textarea } = DOM;
 const EDIT_AND_RESEND = L10N.getStr("netmonitor.summary.editAndResend");
 const RAW_HEADERS = L10N.getStr("netmonitor.summary.rawHeaders");
 const RAW_HEADERS_REQUEST = L10N.getStr("netmonitor.summary.rawHeaders.requestHeaders");
 const RAW_HEADERS_RESPONSE = L10N.getStr("netmonitor.summary.rawHeaders.responseHeaders");
 const HEADERS_EMPTY_TEXT = L10N.getStr("headersEmptyText");
 const HEADERS_FILTER_TEXT = L10N.getStr("headersFilterText");
 const REQUEST_HEADERS = L10N.getStr("requestHeaders");
 const REQUEST_HEADERS_FROM_UPLOAD = L10N.getStr("requestHeadersFromUpload");
@@ -40,16 +45,17 @@ const SUMMARY_VERSION = L10N.getStr("net
  * Lists basic information about the request
  */
 const HeadersPanel = createClass({
   displayName: "HeadersPanel",
 
   propTypes: {
     cloneSelectedRequest: PropTypes.func.isRequired,
     request: PropTypes.object.isRequired,
+    renderValue: PropTypes.func
   },
 
   getInitialState() {
     return {
       rawHeadersOpened: false,
     };
   },
 
@@ -208,15 +214,54 @@ const HeadersPanel = createClass({
           summaryStatus,
           summaryVersion,
           summaryRawHeaders,
         ),
         PropertiesView({
           object,
           filterPlaceHolder: HEADERS_FILTER_TEXT,
           sectionNames: Object.keys(object),
+          renderValue
         }),
       )
     );
   }
 });
 
+function onLearnMoreClick(e, headerDocURL) {
+  e.stopPropagation();
+  e.preventDefault();
+
+  let win = Services.wm.getMostRecentWindow(gDevTools.chromeWindowType);
+  win.openUILinkIn(headerDocURL, "tab");
+}
+
+function renderValue(props) {
+  const { member, value } = props;
+
+  if (typeof value !== "string") {
+    return null;
+  }
+
+  let headerDocURL = HeadersMDN.getURL(member.name);
+
+  return (
+    div({ className: "treeValueCellDivider" },
+      Rep(Object.assign(props, {
+        // FIXME: A workaround for the issue in StringRep
+        // Force StringRep to crop the text everytime
+        member: Object.assign({}, member, { open: false }),
+        mode: MODE.TINY,
+        cropLimit: 60,
+      })),
+      headerDocURL ?
+        a({
+          className: "learn-more-link",
+          title: headerDocURL,
+          onClick: (e) => onLearnMoreClick(e, headerDocURL),
+        }, `[${L10N.getStr("netmonitor.headers.learnMore")}]`)
+        :
+        null
+    )
+  );
+}
+
 module.exports = HeadersPanel;

--- a/devtools/client/netmonitor/shared/components/moz.build
+++ b/devtools/client/netmonitor/shared/components/moz.build
@@ -1,16 +1,17 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 DevToolsModules(
     'cookies-panel.js',
     'details-panel.js',
     'editor.js',
+    'headers-mdn.js',
     'headers-panel.js',
     'params-panel.js',
     'preview-panel.js',
     'properties-view.js',
     'response-panel.js',
     'security-panel.js',
     'timings-panel.js',
 )

--- a/devtools/client/netmonitor/test/browser.ini
+++ b/devtools/client/netmonitor/test/browser.ini
@@ -93,16 +93,17 @@ subsuite = clipboard
 skip-if = (os == 'linux' && bits == 32 && debug) # bug 1328915, disable linux32 debug devtools for timeouts
 [browser_net_copy_as_curl.js]
 subsuite = clipboard
 skip-if = (os == 'linux' && bits == 32 && debug) # bug 1328915, disable linux32 debug devtools for timeouts
 [browser_net_cors_requests.js]
 [browser_net_cyrillic-01.js]
 [browser_net_cyrillic-02.js]
 [browser_net_frame.js]
+[browser_net_header-docs.js]
 skip-if = (os == 'linux' && debug && bits == 32) # Bug 1321434
 [browser_net_filter-01.js]
 skip-if = (os == 'linux' && debug && bits == 32) # Bug 1303439
 [browser_net_filter-02.js]
 [browser_net_filter-03.js]
 [browser_net_filter-04.js]
 [browser_net_footer-summary.js]
 [browser_net_html-preview.js]

new file mode 100644
--- /dev/null
+++ b/devtools/client/netmonitor/test/browser_net_header-docs.js
@@ -0,0 +1,56 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const HeadersMDN = require("devtools/client/netmonitor/shared/components/headers-mdn");
+
+/**
+ * Tests if "Learn More" links are correctly displayed
+ * next to headers.
+ */
+add_task(function* () {
+  let { tab, monitor } = yield initNetMonitor(POST_DATA_URL);
+  info("Starting test... ");
+
+  let { document, NetMonitorView } = monitor.panelWin;
+  let { RequestsMenu } = NetMonitorView;
+
+  RequestsMenu.lazyUpdate = false;
+
+  let wait = waitForNetworkEvents(monitor, 0, 2);
+  yield ContentTask.spawn(tab.linkedBrowser, {}, function* () {
+    content.wrappedJSObject.performRequests();
+  });
+  yield wait;
+
+  let origItem = RequestsMenu.getItemAtIndex(0);
+  RequestsMenu.selectedItem = origItem;
+
+  EventUtils.sendMouseEvent({ type: "click" },
+    document.querySelectorAll(".request-list-item")[0]);
+
+  testShowLearnMore(origItem);
+
+  return teardown(monitor);
+
+  /*
+   * Tests that a "Learn More" button is only shown if
+   * and only if a header is documented in MDN.
+   */
+  function testShowLearnMore(data) {
+    document.querySelectorAll(".properties-view .treeRow.stringRow").forEach((rowEl, index) => {
+      let headerName = rowEl.querySelectorAll(".treeLabelCell .treeLabel")[0].textContent;
+      let headerDocURL = HeadersMDN.getURL(headerName);
+      let learnMoreEl = rowEl.querySelectorAll(".treeValueCell .learn-more-link");
+
+      if (headerDocURL === null) {
+        ok(learnMoreEl.length === 0,
+          "undocumented header does not include a \"Learn More\" button");
+      } else {
+        ok(learnMoreEl[0].getAttribute("title") === headerDocURL,
+          "documented header includes a \"Learn More\" button with a link to MDN");
+      }
+    });
+  }
+});

--- a/devtools/client/shared/components/tree/tree-view.css
+++ b/devtools/client/shared/components/tree/tree-view.css
@@ -72,16 +72,33 @@
   text-decoration: underline;
 }
 
 /* Filtering */
 .treeTable .treeRow.hidden {
   display: none;
 }
 
+.treeTable .treeValueCellDivider {
+  display: flex;
+  flex-wrap: wrap;
+  justify-content: space-between;
+}
+
+/* Learn More link */
+.treeTable .treeValueCell .learn-more-link {
+  color: var(--theme-highlight-blue);
+  cursor: pointer;
+  margin: 0 5px;
+}
+
+.treeTable .treeValueCell .learn-more-link:hover {
+  text-decoration: underline;
+}
+
 /******************************************************************************/
 /* Toggle Icon */
 
 .treeTable .treeRow .treeIcon {
   height: 14px;
   width: 14px;
   font-size: 10px; /* Set the size of loading spinner */
   display: inline-block;