diff --git a/browser/components/preferences/in-content-new/main.js b/browser/components/preferences/in-content-new/main.js
index fbd86fb5f088..4c82838942f2 100644
--- a/browser/components/preferences/in-content-new/main.js
+++ b/browser/components/preferences/in-content-new/main.js
@@ -1118,13 +1118,22 @@ var gMainPane = {
     let defaultPerformancePref =
       document.getElementById("browser.preferences.defaultPerformanceSettings.enabled");
     let performanceSettings = document.getElementById("performanceSettings");
+    let processCountPref = document.getElementById("dom.ipc.processCount");
     if (defaultPerformancePref.value) {
-      let processCountPref = document.getElementById("dom.ipc.processCount");
       let accelerationPref = document.getElementById("layers.acceleration.disabled");
+      // Unset the value so process count will be decided by e10s rollout.
       processCountPref.value = processCountPref.defaultValue;
       accelerationPref.value = accelerationPref.defaultValue;
       performanceSettings.hidden = true;
     } else {
+      let e10sRolloutProcessCountPref =
+        document.getElementById("dom.ipc.processCount.web");
+      // Take the e10s rollout value as the default value (if it exists),
+      // but don't overwrite the user set value.
+      if (e10sRolloutProcessCountPref.value &&
+          processCountPref.value == processCountPref.defaultValue) {
+        processCountPref.value = e10sRolloutProcessCountPref.value;
+      }
       performanceSettings.hidden = false;
     }
   },
@@ -1132,12 +1141,16 @@ var gMainPane = {
   buildContentProcessCountMenuList() {
     if (gMainPane.isE10SEnabled()) {
       let processCountPref = document.getElementById("dom.ipc.processCount");
+      let e10sRolloutProcessCountPref =
+        document.getElementById("dom.ipc.processCount.web");
+      let defaultProcessCount =
+        e10sRolloutProcessCountPref.value || processCountPref.defaultValue;
       let bundlePreferences = document.getElementById("bundlePreferences");
       let label = bundlePreferences.getFormattedString("defaultContentProcessCount",
-        [processCountPref.defaultValue]);
+        [defaultProcessCount]);
       let contentProcessCount =
         document.querySelector(`#contentProcessCount > menupopup >
-                                menuitem[value="${processCountPref.defaultValue}"]`);
+                                menuitem[value="${defaultProcessCount}"]`);
       contentProcessCount.label = label;
 
       document.getElementById("limitContentProcess").disabled = false;
diff --git a/browser/components/preferences/in-content-new/main.xul b/browser/components/preferences/in-content-new/main.xul
index 5c43a11a5f9b..29e2edea79ad 100644
--- a/browser/components/preferences/in-content-new/main.xul
+++ b/browser/components/preferences/in-content-new/main.xul
@@ -184,6 +184,10 @@
               name="dom.ipc.processCount"
               type="int"/>
 
+  <preference id="dom.ipc.processCount.web"
+              name="dom.ipc.processCount.web"
+              type="int"/>
+
   <preference id="layers.acceleration.disabled"
               name="layers.acceleration.disabled"
               type="bool"
diff --git a/browser/components/preferences/in-content/main.js b/browser/components/preferences/in-content/main.js
index 36a51b07d94a..02a4080fef0a 100644
--- a/browser/components/preferences/in-content/main.js
+++ b/browser/components/preferences/in-content/main.js
@@ -429,13 +429,22 @@ var gMainPane = {
     let defaultPerformancePref =
       document.getElementById("browser.preferences.defaultPerformanceSettings.enabled");
     let performanceSettings = document.getElementById("performanceSettings");
+    let processCountPref = document.getElementById("dom.ipc.processCount");
     if (defaultPerformancePref.value) {
-      let processCountPref = document.getElementById("dom.ipc.processCount");
       let accelerationPref = document.getElementById("layers.acceleration.disabled");
+      // Unset the value so process count will be decided by e10s rollout.
       processCountPref.value = processCountPref.defaultValue;
       accelerationPref.value = accelerationPref.defaultValue;
       performanceSettings.hidden = true;
     } else {
+      let e10sRolloutProcessCountPref =
+        document.getElementById("dom.ipc.processCount.web");
+      // Take the e10s rollout value as the default value (if it exists),
+      // but don't overwrite the user set value.
+      if (e10sRolloutProcessCountPref.value &&
+          processCountPref.value == processCountPref.defaultValue) {
+        processCountPref.value = e10sRolloutProcessCountPref.value;
+      }
       performanceSettings.hidden = false;
     }
   },
@@ -443,12 +452,16 @@ var gMainPane = {
   buildContentProcessCountMenuList() {
     if (gMainPane.isE10SEnabled()) {
       let processCountPref = document.getElementById("dom.ipc.processCount");
+      let e10sRolloutProcessCountPref =
+        document.getElementById("dom.ipc.processCount.web");
+      let defaultProcessCount =
+        e10sRolloutProcessCountPref.value || processCountPref.defaultValue;
       let bundlePreferences = document.getElementById("bundlePreferences");
       let label = bundlePreferences.getFormattedString("defaultContentProcessCount",
-        [processCountPref.defaultValue]);
+        [defaultProcessCount]);
       let contentProcessCount =
         document.querySelector(`#contentProcessCount > menupopup >
-                                menuitem[value="${processCountPref.defaultValue}"]`);
+                                menuitem[value="${defaultProcessCount}"]`);
       contentProcessCount.label = label;
 
       document.getElementById("limitContentProcess").disabled = false;
diff --git a/browser/components/preferences/in-content/main.xul b/browser/components/preferences/in-content/main.xul
index e2b875d915f3..7167b554bd2c 100644
--- a/browser/components/preferences/in-content/main.xul
+++ b/browser/components/preferences/in-content/main.xul
@@ -119,6 +119,10 @@
               name="dom.ipc.processCount"
               type="int"/>
 
+  <preference id="dom.ipc.processCount.web"
+              name="dom.ipc.processCount.web"
+              type="int"/>
+
   <preference id="layers.acceleration.disabled"
               name="layers.acceleration.disabled"
               type="bool"