--- a/devtools/client/aboutdebugging/components/workers/multi-e10s-warning.js
+++ b/devtools/client/aboutdebugging/components/workers/multi-e10s-warning.js
@@ -21,17 +21,17 @@ loader.lazyRequireGetter(this, "Debugger
 
 const Strings = Services.strings.createBundle("chrome://devtools/locale/aboutdebugging.properties");
 const MULTI_OPT_OUT_PREF = "dom.ipc.multiOptOut";
 
 module.exports = createClass({
   displayName: "multiE10SWarning",
 
   onUpdatePreferenceClick() {
-    let message = Strings.GetStringFromName("multiProcessWarningConfirmUpdate");
+    let message = Strings.GetStringFromName("multiProcessWarningConfirmUpdate2");
     if (window.confirm(message)) {
       // Disable multi until at least the next experiment.
       Services.prefs.setIntPref(MULTI_OPT_OUT_PREF,
                                 Services.appinfo.E10S_MULTI_EXPERIMENT);
       // Restart the browser.
       Services.startup.quit(Ci.nsIAppStartup.eAttemptQuit | Ci.nsIAppStartup.eRestart);
     }
   },
@@ -43,20 +43,20 @@ module.exports = createClass({
       },
       dom.div(
         {},
         dom.div({ className: "warning" }),
         dom.b({}, Strings.GetStringFromName("multiProcessWarningTitle"))
       ),
       dom.div(
         {},
-        Strings.GetStringFromName("multiProcessWarningMessage")
+        Strings.GetStringFromName("multiProcessWarningMessage2")
       ),
       dom.button(
         {
           className: "update-button",
           onClick: this.onUpdatePreferenceClick,
         },
-        Strings.GetStringFromName("multiProcessWarningUpdateLink")
+        Strings.GetStringFromName("multiProcessWarningUpdateLink2")
       )
     );
   },
 });

--- a/devtools/client/aboutdebugging/components/workers/panel.js
+++ b/devtools/client/aboutdebugging/components/workers/panel.js
@@ -26,16 +26,17 @@ loader.lazyRequireGetter(this, "Debugger
   "devtools/shared/client/main", true);
 
 const Strings = Services.strings.createBundle(
   "chrome://devtools/locale/aboutdebugging.properties");
 
 const WorkerIcon = "chrome://devtools/skin/images/debugging-workers.svg";
 const MORE_INFO_URL = "https://developer.mozilla.org/en-US/docs/Tools/about%3Adebugging";
 const PROCESS_COUNT_PREF = "dom.ipc.processCount";
+const MULTI_OPTOUT_PREF = "dom.ipc.multiOptOut";
 
 module.exports = createClass({
   displayName: "WorkersPanel",
 
   propTypes: {
     client: PropTypes.instanceOf(DebuggerClient).isRequired,
     id: PropTypes.string.isRequired
   },
@@ -53,35 +54,49 @@ module.exports = createClass({
 
   componentDidMount() {
     let client = this.props.client;
     client.addListener("workerListChanged", this.updateWorkers);
     client.addListener("serviceWorkerRegistrationListChanged", this.updateWorkers);
     client.addListener("processListChanged", this.updateWorkers);
     client.addListener("registration-changed", this.updateWorkers);
 
+    // Some notes about these observers:
+    // - nsIPrefBranch.addObserver observes prefixes. In reality, watching
+    //   PROCESS_COUNT_PREF watches two separate prefs:
+    //   dom.ipc.processCount *and* dom.ipc.processCount.web. Because these
+    //   are the two ways that we control the number of content processes,
+    //   that works perfectly fine.
+    // - The user might opt in or out of multi by setting the multi opt out
+    //   pref. That affects whether we need to show our warning, so we need to
+    //   update our state when that pref changes.
+    // - In all cases, we don't have to manually check which pref changed to
+    //   what. The platform code in nsIXULRuntime.maxWebProcessCount does all
+    //   of that for us.
     Services.prefs.addObserver(PROCESS_COUNT_PREF, this.updateMultiE10S);
+    Services.prefs.addObserver(MULTI_OPTOUT_PREF, this.updateMultiE10S);
 
     this.updateMultiE10S();
     this.updateWorkers();
   },
 
   componentWillUnmount() {
     let client = this.props.client;
     client.removeListener("processListChanged", this.updateWorkers);
     client.removeListener("serviceWorkerRegistrationListChanged", this.updateWorkers);
     client.removeListener("workerListChanged", this.updateWorkers);
     client.removeListener("registration-changed", this.updateWorkers);
 
     Services.prefs.removeObserver(PROCESS_COUNT_PREF, this.updateMultiE10S);
+    Services.prefs.removeObserver(MULTI_OPTOUT_PREF, this.updateMultiE10S);
   },
 
   updateMultiE10S() {
     // We watch the pref but set the state based on
-    // nsIXULRuntime::maxWebProcessCount.
+    // nsIXULRuntime.maxWebProcessCount.
     let processCount = Services.appinfo.maxWebProcessCount;
     this.setState({ processCount });
   },
 
   updateWorkers() {
     let workers = this.getInitialState().workers;
 
     getWorkerForms(this.props.client).then(forms => {

--- a/devtools/client/locales/en-US/aboutdebugging.properties
+++ b/devtools/client/locales/en-US/aboutdebugging.properties
@@ -123,19 +123,19 @@ configurationIsNotCompatible = Your brow
 # LOCALIZATION NOTE (multiProcessWarningTitle):
 # This string is displayed as a warning message on top of the about:debugging#workers
 # page when multi-e10s is enabled
 multiProcessWarningTitle = Service Worker debugging is not compatible with multiple content processes at the moment.
 
 # LOCALIZATION NOTE (multiProcessWarningMessage):
 # This string is displayed in the warning section for multi-e10s in
 # about:debugging#workers
-multiProcessWarningMessage = The preference “dom.ipc.processCount” can be set to 1 to force a single content process.
+multiProcessWarningMessage2 = The preference “dom.ipc.multiOptOut” can be modified to force a single content process for the current version.
 
 # LOCALIZATION NOTE (multiProcessWarningLink):
 # This string is the text content of a link in the warning section for multi-e10s in
 # about:debugging#workers. The link updates the pref and restarts the browser.
-multiProcessWarningUpdateLink = Set dom.ipc.processCount to 1
+multiProcessWarningUpdateLink2 = Opt out of multiple content processes
 
 # LOCALIZATION NOTE (multiProcessWarningConfirmUpdate):
 # This string is displayed as a confirmation message when the user clicks on
 # the multiProcessWarningUpdateLink in about:debugging#workers
-multiProcessWarningConfirmUpdate = Set “dom.ipc.processCount” to 1 and restart the browser?
+multiProcessWarningConfirmUpdate2 = Opt out of multiple processes?