--- a/browser/components/migration/MigrationUtils.jsm
+++ b/browser/components/migration/MigrationUtils.jsm
@@ -37,16 +37,17 @@ ChromeUtils.defineModuleGetter(this, "Wi
 ChromeUtils.defineModuleGetter(this, "setTimeout",
                                "resource://gre/modules/Timer.jsm");
 
 var gMigrators = null;
 var gProfileStartup = null;
 var gMigrationBundle = null;
 var gPreviousDefaultBrowserKey = "";
 
+let gForceExitSpinResolve = false;
 let gKeepUndoData = false;
 let gUndoData = null;
 
 XPCOMUtils.defineLazyGetter(this, "gAvailableMigratorKeys", function() {
   if (AppConstants.platform == "win") {
     return [
       "firefox", "edge", "ie", "chrome", "chromium", "360se",
       "canary",
@@ -647,32 +648,39 @@ this.MigrationUtils = Object.freeze({
 
   get _migrators() {
     if (!gMigrators) {
       gMigrators = new Map();
     }
     return gMigrators;
   },
 
+  forceExitSpinResolve: function MU_forceExitSpinResolve() {
+    gForceExitSpinResolve = true;
+  },
+
   spinResolve: function MU_spinResolve(promise) {
     if (!(promise instanceof Promise)) {
       return promise;
     }
     let done = false;
     let result = null;
     let error = null;
+    gForceExitSpinResolve = false;
     promise.catch(e => {
       error = e;
     }).then(r => {
       result = r;
       done = true;
     });
 
-    Services.tm.spinEventLoopUntil(() => done);
-    if (error) {
+    Services.tm.spinEventLoopUntil(() => done || gForceExitSpinResolve);
+    if (!done) {
+      throw new Error("Forcefully exited event loop.");
+    } else if (error) {
       throw error;
     } else {
       return result;
     }
   },
 
   /*
    * Returns the migrator for the given source, if any data is available

--- a/browser/components/migration/content/migration.js
+++ b/browser/components/migration/content/migration.js
@@ -61,29 +61,27 @@ var MigrationWizard = { /* exported Migr
     os.removeObserver(this, "Migration:ItemError");
     os.removeObserver(this, "Migration:Ended");
     MigrationUtils.finishMigration();
   },
 
   spinResolve(promise) {
     let canAdvance = this._wiz.canAdvance;
     let canRewind = this._wiz.canRewind;
-    let canCancel = this._canCancel;
     this._wiz.canAdvance = false;
     this._wiz.canRewind = false;
-    this._canCancel = false;
     let result = MigrationUtils.spinResolve(promise);
     this._wiz.canAdvance = canAdvance;
     this._wiz.canRewind = canRewind;
-    this._canCancel = canCancel;
     return result;
   },
 
   onWizardCancel() {
-    return this._canCancel;
+    MigrationUtils.forceExitSpinResolve();
+    return true;
   },
 
   // 1 - Import Source
   onImportSourcePageShow() {
     // Show warning message to close the selected browser when needed
     let toggleCloseBrowserWarning = () => {
       let visibility = "hidden";
       if (group.selectedItem.id != "nothing") {

--- a/browser/components/migration/content/migration.xul
+++ b/browser/components/migration/content/migration.xul
@@ -10,17 +10,18 @@
 <wizard id="migrationWizard"
         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
         windowtype="Browser:MigrationWizard"
         title="&migrationWizard.title;"
         onload="MigrationWizard.init()"
         onunload="MigrationWizard.uninit()"
         style="width: 40em;"
         buttons="accept,cancel"
-        branded="true">
+        branded="true"
+        onwizardcancel="return MigrationWizard.onWizardCancel();">
 
   <script type="application/javascript" src="chrome://browser/content/migration/migration.js"/>
 
   <wizardpage id="importSource" pageid="importSource" next="selectProfile"
               label="&importSource.title;"
               onpageadvanced="return MigrationWizard.onImportSourcePageAdvanced();">
 #ifdef XP_WIN
     <description id="importAll" control="importSourceGroup">&importFrom.label;</description>