--- a/browser/base/content/test/tabs/browser.ini
+++ b/browser/base/content/test/tabs/browser.ini
@@ -1,9 +1,14 @@
 [DEFAULT]
+prefs =
+    # With Fission enabled, this directory spawns many child processes, which
+    # somehow results in frequent shutdown leaks. Reuse the content processes
+    # to avoid this.
+    dom.ipc.keepProcessesAlive.webIsolated.perOrigin=1
 support-files =
   head.js
   dummy_page.html
   ../general/audio.ogg
   file_mediaPlayback.html
   test_process_flags_chrome.html
 
 [browser_accessibility_indicator.js]

--- a/browser/components/extensions/test/browser/browser.ini
+++ b/browser/components/extensions/test/browser/browser.ini
@@ -1,14 +1,18 @@
 [DEFAULT]
 tags = webextensions
 prefs =
     # We don't want to reset this at the end of the test, so that we don't have
     # to spawn a new extension child process for each test unit.
     dom.ipc.keepProcessesAlive.extension=1
+    # With Fission enabled, this directory spawns many child processes, which
+    # somehow results in frequent leaks and shutdown hangs. Reuse the content
+    # processes to avoid this.
+    dom.ipc.keepProcessesAlive.webIsolated.perOrigin=1
     dom.animations-api.core.enabled=true
     dom.animations-api.timelines.enabled=true
     plugin.load_flash_only=false
 support-files =
   head.js
   head_devtools.js
   silence.ogg
   head_browserAction.js

--- a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_rememberprompt.js
+++ b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_rememberprompt.js
@@ -1,18 +1,23 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 // This test makes sure that the geolocation prompt does not show a remember
 // control inside the private browsing mode.
 
+// This test leaks intermittently with Fission. Make it behave more like
+// non-Fission e10s tests to try to avoid them.
 add_task(async function setup() {
   await SpecialPowers.pushPrefEnv({
-    set: [["dom.vr.always_support_vr", true]],
+    set: [
+      ["dom.ipc.keepProcessesAlive.webIsolated.perOrigin", 1],
+      ["dom.vr.always_support_vr", true],
+    ],
   });
 });
 
 add_task(async function test() {
   function checkPrompt(aURL, aName, aPrivateMode, aWindow) {
     return (async function() {
       aWindow.gBrowser.selectedTab = BrowserTestUtils.addTab(
         aWindow.gBrowser,

--- a/browser/components/uitour/test/browser.ini
+++ b/browser/components/uitour/test/browser.ini
@@ -1,9 +1,14 @@
 [DEFAULT]
+prefs =
+    # With Fission enabled, this directory spawns many child processes, which
+    # somehow results in frequent shutdown leaks and hangs. Reuse the content
+    # processes to avoid this.
+    dom.ipc.keepProcessesAlive.webIsolated.perOrigin=1
 support-files =
   head.js
   image.png
   uitour.html
   ../UITour-lib.js
 
 [browser_backgroundTab.js]
 [browser_closeTab.js]

--- a/browser/components/urlbar/tests/browser/browser.ini
+++ b/browser/components/urlbar/tests/browser/browser.ini
@@ -2,16 +2,21 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 [DEFAULT]
 support-files =
   dummy_page.html
   head.js
   head-common.js
+prefs =
+    # With Fission enabled, these tests spawns many child processes, which
+    # somehow results in frequent shutdown leaks. Reuse the content processes
+    # to avoid this.
+    dom.ipc.keepProcessesAlive.webIsolated.perOrigin=1
 
 [browser_aboutHomeLoading.js]
 [browser_action_searchengine.js]
 [browser_action_searchengine_alias.js]
 [browser_autocomplete_a11y_label.js]
 support-files =
   searchSuggestionEngine.xml
   searchSuggestionEngine.sjs

--- a/toolkit/components/reader/test/browser.ini
+++ b/toolkit/components/reader/test/browser.ini
@@ -1,9 +1,14 @@
 [DEFAULT]
+prefs =
+    # With Fission enabled, this directory spawns many child processes, which
+    # somehow results in frequent shutdown leaks. Reuse the content processes
+    # to avoid this. See bug 1594572.
+    dom.ipc.keepProcessesAlive.webIsolated.perOrigin=1
 support-files = head.js
 [browser_readerMode.js]
 support-files =
   readerModeNonArticle.html
   readerModeArticle.html
   readerModeArticleHiddenNodes.html
 [browser_readerMode_hidden_nodes.js]
 support-files =