--- a/browser/base/content/test/general/browser_devedition.js
+++ b/browser/base/content/test/general/browser_devedition.js
@@ -19,17 +19,19 @@ registerCleanupFunction(() => {
 });
 
 function test() {
   waitForExplicitFinish();
   startTests();
 }
 
 function startTests() {
-  ok (!DevEdition.styleSheet, "There is no devedition style sheet by default.");
+  info ("Setting browser.devedition.theme.enabled to false.");
+  Services.prefs.setBoolPref(PREF_DEVEDITION_THEME, false);
+  ok (!DevEdition.styleSheet, "There is no devedition style sheet when the pref is false.");
 
   info ("Setting browser.devedition.theme.enabled to true.");
   Services.prefs.setBoolPref(PREF_DEVEDITION_THEME, true);
   ok (DevEdition.styleSheet, "There is a devedition stylesheet when no themes are applied and pref is set.");
 
   info ("Adding a lightweight theme.");
   Services.prefs.setBoolPref(PREF_LWTHEME, true);
   ok (!DevEdition.styleSheet, "The devedition stylesheet has been removed when a lightweight theme is applied.");
@@ -48,16 +50,17 @@ function startTests() {
   Services.prefs.clearUserPref(PREF_THEME);
   ok (DevEdition.styleSheet, "The devedition stylesheet is still here when a complete theme is removed.");
 
   info ("Setting browser.devedition.theme.enabled to false.");
   Services.prefs.setBoolPref(PREF_DEVEDITION_THEME, false);
   ok (!DevEdition.styleSheet, "The devedition stylesheet has been removed.");
 
   info ("Checking :root attributes based on devtools theme.");
+  Services.prefs.setCharPref(PREF_DEVTOOLS_THEME, "light");
   is (document.documentElement.getAttribute("devtoolstheme"), "light",
     "The documentElement has an attribute based on devtools theme.");
   Services.prefs.setCharPref(PREF_DEVTOOLS_THEME, "dark");
   is (document.documentElement.getAttribute("devtoolstheme"), "dark",
     "The documentElement has an attribute based on devtools theme.");
   Services.prefs.setCharPref(PREF_DEVTOOLS_THEME, "light");
   is (document.documentElement.getAttribute("devtoolstheme"), "light",
     "The documentElement has an attribute based on devtools theme.");