diff --git a/docshell/test/chrome/chrome.ini b/docshell/test/chrome/chrome.ini
index ce5e44c72cb2..6a7cd66c7109 100644
--- a/docshell/test/chrome/chrome.ini
+++ b/docshell/test/chrome/chrome.ini
@@ -84,6 +84,11 @@ skip-if = true # Bug 1026815,Bug 1546159
 [test_bug89419.xhtml]
 [test_bug909218.html]
 [test_bug92598.xhtml]
+[test_open_and_immediately_close_opener.html]
+# This bug only manifests in the non-e10s window open codepath. The test
+# should be updated to make sure it still opens a new window in the parent
+# process if and when we start running chrome mochitests with e10s enabled.
+skip-if = e10s
 [test_mozFrameType.xhtml]
 [test_viewsource_forbidden_in_iframe.xhtml]
 skip-if = true # bug 1019315
diff --git a/docshell/test/chrome/test_open_and_immediately_close_opener.html b/docshell/test/chrome/test_open_and_immediately_close_opener.html
new file mode 100644
index 000000000000..bb5f6f054df1
--- /dev/null
+++ b/docshell/test/chrome/test_open_and_immediately_close_opener.html
@@ -0,0 +1,54 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Test for Bug 1702678</title>
+  <meta charset="utf-8">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1702678">Mozilla Bug 1702678</a>
+
+<script type="application/javascript">
+"use strict";
+
+const HTML = `
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <script>
+    // We need to queue a promise reaction job whilch will close the window
+    // during the nested event loop spun up by the window opening code.
+    Promise.resolve().then(() => {
+      window.close();
+    });
+    window.open("data:text/html,Hello");
+  <\/script>
+</head>
+</html>
+`;
+
+add_task(async function() {
+  // This bug only manifests when opening tabs in new windows.
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.link.open_newwindow", 2]],
+  });
+
+  // Create a window in a new BrowsingContextGroup so that it will be the last
+  // window in the group when it closes, and the group will be destroyed.
+  window.open(`data:text/html,${encodeURIComponent(HTML)}`, "", "noopener");
+
+  // Make a few trips through the event loop to ensure we've had a chance to
+  // open and close the relevant windows.
+  for (let i = 0; i < 10; i++) {
+    await new Promise(resolve => setTimeout(resolve, 0));
+  }
+
+  ok(true, "We didn't crash");
+});
+</script>
+
+</body>
+</html>
+
diff --git a/dom/base/nsFrameLoader.cpp b/dom/base/nsFrameLoader.cpp
index 7202ca16518a..bbb1a9e01a67 100644
--- a/dom/base/nsFrameLoader.cpp
+++ b/dom/base/nsFrameLoader.cpp
@@ -288,8 +288,23 @@ static already_AddRefed<BrowsingContext> CreateBrowsingContext(
   RefPtr<BrowsingContext> opener;
   if (aOpenWindowInfo && !aOpenWindowInfo->GetForceNoOpener()) {
     opener = aOpenWindowInfo->GetParent();
-    // Must create BrowsingContext with opener in-process.
-    MOZ_ASSERT_IF(opener, opener->IsInProcess());
+    if (opener) {
+      // Must create BrowsingContext with opener in-process.
+      MOZ_ASSERT(opener->IsInProcess());
+
+      // This can only happen when the opener was closed from a nested event
+      // loop in the window provider code, and only when the open was triggered
+      // by a non-e10s tab, and the new tab is being opened in a new browser
+      // window. Since it is a corner case among corner cases, and the opener
+      // window will appear to be null to consumers after it is discarded
+      // anyway, just drop the opener entirely.
+      if (opener->IsDiscarded()) {
+        NS_WARNING(
+            "Opener was closed from a nested event loop in the parent process. "
+            "Please fix this.");
+        opener = nullptr;
+      }
+    }
   }
 
   RefPtr<nsGlobalWindowInner> parentInner =
diff --git a/toolkit/components/windowwatcher/nsWindowWatcher.cpp b/toolkit/components/windowwatcher/nsWindowWatcher.cpp
index 027f269e5e54..61ab895bfb89 100644
--- a/toolkit/components/windowwatcher/nsWindowWatcher.cpp
+++ b/toolkit/components/windowwatcher/nsWindowWatcher.cpp
@@ -986,8 +986,18 @@ nsresult nsWindowWatcher::OpenWindowInternal(
     // when its BrowsingContext was created, in order to ensure that the context
     // is loaded within the correct BrowsingContextGroup.
     if (windowIsNew && newBC->IsContent()) {
-      MOZ_RELEASE_ASSERT(newBC->GetOpenerId() == parentBC->Id());
-      MOZ_RELEASE_ASSERT(!!parentBC == newBC->HadOriginalOpener());
+      if (parentBC->IsDiscarded()) {
+        // If the parent BC was discarded in a nested event loop before we got
+        // to this point, we can't set it as the opener. Ideally we would still
+        // set `HadOriginalOpener()` in that case, but that's somewhat
+        // nontrivial, and not worth the effort given the nature of the corner
+        // case (see comment in `nsFrameLoader::CreateBrowsingContext`.
+        MOZ_RELEASE_ASSERT(newBC->GetOpenerId() == parentBC->Id() ||
+                           newBC->GetOpenerId() == 0);
+      } else {
+        MOZ_RELEASE_ASSERT(newBC->GetOpenerId() == parentBC->Id());
+        MOZ_RELEASE_ASSERT(newBC->HadOriginalOpener());
+      }
     } else {
       // Update the opener for an existing or chrome BC.
       newBC->SetOpener(parentBC);
