--- a/dom/base/test/browser.ini
+++ b/dom/base/test/browser.ini
@@ -23,18 +23,16 @@ support-files =
   file_webaudioLoop.html
   plugin.js
 
 [browser_bug593387.js]
 [browser_bug902350.js]
 tags = mcb
 [browser_bug1011748.js]
 [browser_bug1058164.js]
-[browser_force_process_selector.js]
-skip-if = !e10s # this only makes sense with e10s-multi
 [browser_messagemanager_loadprocessscript.js]
 [browser_messagemanager_targetframeloader.js]
 [browser_messagemanager_unload.js]
 [browser_pagehide_on_tab_close.js]
 skip-if = e10s # this tests non-e10s behavior. it's not expected to work in e10s.
 [browser_state_notifications.js]
 skip-if = true # Bug 1271028
 [browser_use_counters.js]

deleted file mode 100644
--- a/dom/base/test/browser_force_process_selector.js
+++ /dev/null
@@ -1,36 +0,0 @@
-"use strict";
-
-// Make sure that BTU.withNewTab({ ..., forceNewProcess: true }) loads
-// new tabs in their own process.
-async function spawnNewAndTest(recur, pids) {
-  await BrowserTestUtils.withNewTab({ gBrowser, url: "about:blank", forceNewProcess: true },
-                                    function* (browser) {
-      // Make sure our new browser is in its own process.
-      let newPid = browser.frameLoader.tabParent.osPid;
-      ok(!pids.has(newPid), "new tab is in its own process");
-      pids.add(newPid);
-
-      if (recur) {
-        yield spawnNewAndTest(recur - 1, pids);
-      } else {
-        yield BrowserTestUtils.withNewTab({ gBrowser, url: "about:blank" }, function* (browser) {
-          // This browser should share a PID with one of the existing tabs.
-          // This is a todo because the process we end up using is actually
-          // an extra process that gets started early in startup and not one
-          // of the ones we use for the tabs.
-          todo(pids.has(browser.frameLoader.tabParent.osPid),
-               "we should be reusing processes if not asked to force the " +
-               "tab into its own process");
-        });
-      }
-  });
-}
-
-add_task(async function test() {
-  let curPid = gBrowser.selectedBrowser.frameLoader.tabParent.osPid;
-  let maxCount = Services.prefs.getIntPref("dom.ipc.processCount");
-
-  // Use at least one more tab than max processes or at least 5 to make this
-  // test interesting.
-  await spawnNewAndTest(Math.max(maxCount + 1, 5), new Set([ curPid ]));
-});

--- a/testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm
+++ b/testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm
@@ -28,39 +28,16 @@ Cu.import("resource://testing-common/Con
 Cc["@mozilla.org/globalmessagemanager;1"]
   .getService(Ci.nsIMessageListenerManager)
   .loadFrameScript(
     "chrome://mochikit/content/tests/BrowserTestUtils/content-utils.js", true);
 
 XPCOMUtils.defineLazyModuleGetter(this, "E10SUtils",
   "resource:///modules/E10SUtils.jsm");
 
-const PROCESSSELECTOR_CONTRACTID = "@mozilla.org/ipc/processselector;1";
-const DEFAULT_PROCESSSELECTOR_CID =
-  Components.ID(Cc[PROCESSSELECTOR_CONTRACTID].number);
-const OUR_PROCESSSELECTOR_CID =
-  Components.ID("{f9746211-3d53-4465-9aeb-ca0d96de0253}");
-
-// A process selector that always asks for a new process.
-function NewProcessSelector() {
-}
-
-NewProcessSelector.prototype = {
-  classID: OUR_PROCESSSELECTOR_CID,
-  QueryInterface: XPCOMUtils.generateQI([Ci.nsIContentProcessProvider]),
-
-  provideProcess() {
-    return Ci.nsIContentProcessProvider.NEW_PROCESS;
-  }
-};
-
-let registrar = Components.manager.QueryInterface(Ci.nsIComponentRegistrar);
-let selectorFactory = XPCOMUtils._getFactory(NewProcessSelector);
-registrar.registerFactory(OUR_PROCESSSELECTOR_CID, "", null, selectorFactory);
-
 // For now, we'll allow tests to use CPOWs in this module for
 // some cases.
 Cu.permitCPOWsInScope(this);
 
 var gSendCharCount = 0;
 var gSynthesizeKeyCount = 0;
 var gSynthesizeCompositionCount = 0;
 var gSynthesizeCompositionChangeCount = 0;
@@ -95,122 +72,101 @@ this.BrowserTestUtils = {
    */
   withNewTab: Task.async(function* (options, taskFn) {
     if (typeof(options) == "string") {
       options = {
         gBrowser: Services.wm.getMostRecentWindow("navigator:browser").gBrowser,
         url: options
       }
     }
-    let tab = yield BrowserTestUtils.openNewForegroundTab(options);
+    let tab = yield BrowserTestUtils.openNewForegroundTab(options.gBrowser, options.url);
     let originalWindow = tab.ownerGlobal;
     let result = yield taskFn(tab.linkedBrowser);
     let finalWindow = tab.ownerGlobal;
     if (originalWindow == finalWindow && !tab.closing && tab.linkedBrowser) {
       yield BrowserTestUtils.removeTab(tab);
     } else {
       Services.console.logStringMessage(
         "BrowserTestUtils.withNewTab: Tab was already closed before " +
         "removeTab would have been called");
     }
     return Promise.resolve(result);
   }),
 
   /**
    * Opens a new tab in the foreground.
    *
-   * This function takes an options object (which is preferred) or actual
-   * parameters. The names of the options must correspond to the names below.
-   * gBrowser is required and all other options are optional.
-   *
-   * @param {tabbrowser} gBrowser
+   * @param {tabbrowser} tabbrowser
    *        The tabbrowser to open the tab new in.
    * @param {string} opening (or url)
    *        May be either a string URL to load in the tab, or a function that
    *        will be called to open a foreground tab. Defaults to "about:blank".
    * @param {boolean} waitForLoad
    *        True to wait for the page in the new tab to load. Defaults to true.
    * @param {boolean} waitForStateStop
    *        True to wait for the web progress listener to send STATE_STOP for the
    *        document in the tab. Defaults to false.
    * @param {boolean} forceNewProcess
    *        True to force the new tab to load in a new process. Defaults to
    *        false.
+   * NB: tabbrowser may be an options object containing the rest of the
+   *     parameters.
    *
    * @return {Promise}
    *         Resolves when the tab is ready and loaded as necessary.
    * @resolves The new tab.
    */
   openNewForegroundTab(tabbrowser, ...args) {
     let options;
     if (tabbrowser instanceof Ci.nsIDOMXULElement) {
       // tabbrowser is a tabbrowser, read the rest of the arguments from args.
       let [
         opening = "about:blank",
         waitForLoad = true,
         waitForStateStop = false,
-        forceNewProcess = false,
       ] = args;
 
-      options = { opening, waitForLoad, waitForStateStop, forceNewProcess };
+      options = { opening, waitForLoad, waitForStateStop };
     } else {
       if ("url" in tabbrowser && !("opening" in tabbrowser)) {
         tabbrowser.opening = tabbrowser.url;
       }
 
       let {
         opening = "about:blank",
         waitForLoad = true,
         waitForStateStop = false,
-        forceNewProcess = false,
       } = tabbrowser;
 
       tabbrowser = tabbrowser.gBrowser;
-      options = { opening, waitForLoad, waitForStateStop, forceNewProcess };
+      options = { opening, waitForLoad, waitForStateStop };
     }
 
-    let { opening: opening,
-          waitForLoad: aWaitForLoad,
-          waitForStateStop: aWaitForStateStop
-    } = options;
-
-    let promises, tab;
-    try {
-      // If we're asked to force a new process, replace the normal process
-      // selector with one that always asks for a new process.
-      if (options.forceNewProcess) {
-        registrar.registerFactory(OUR_PROCESSSELECTOR_CID, "",
-                                  PROCESSSELECTOR_CONTRACTID, null);
-      }
+    let { opening: opening, waitForLoad: aWaitForLoad, waitForStateStop: aWaitForStateStop } = options;
 
-      promises = [
-        BrowserTestUtils.switchTab(tabbrowser, function () {
-          if (typeof opening == "function") {
-            opening();
-            tab = tabbrowser.selectedTab;
-          }
-          else {
-            tabbrowser.selectedTab = tab = tabbrowser.addTab(opening);
-          }
-        })
-      ];
+    let tab;
+    let promises = [
+      BrowserTestUtils.switchTab(tabbrowser, function () {
+        if (typeof opening == "function") {
+          opening();
+          tab = tabbrowser.selectedTab;
+        }
+        else {
+          tabbrowser.selectedTab = tab = tabbrowser.addTab(opening);
+        }
+      })
+    ];
 
-      if (aWaitForLoad) {
-        promises.push(BrowserTestUtils.browserLoaded(tab.linkedBrowser));
-      }
-      if (aWaitForStateStop) {
-        promises.push(BrowserTestUtils.browserStopped(tab.linkedBrowser));
-      }
-    } finally {
-      // Restore the original process selector, if needed.
-      if (options.forceNewProcess) {
-        registrar.registerFactory(DEFAULT_PROCESSSELECTOR_CID, "",
-                                  PROCESSSELECTOR_CONTRACTID, null);
-      }
+    if (aWaitForLoad) {
+      promises.push(BrowserTestUtils.browserLoaded(tab.linkedBrowser));
     }
+    if (aWaitForStateStop) {
+      promises.push(BrowserTestUtils.browserStopped(tab.linkedBrowser));
+    }
+
     return Promise.all(promises).then(() => tab);
   },
 
   /**
    * Switches to a tab and resolves when it is ready.
    *
    * @param {tabbrowser} tabbrowser
    *        The tabbrowser.