diff --git a/browser/base/content/tabbrowser.js b/browser/base/content/tabbrowser.js
index 3c25a0389c34..b7e0f7d16ea6 100644
--- a/browser/base/content/tabbrowser.js
+++ b/browser/base/content/tabbrowser.js
@@ -6202,10 +6202,13 @@
           // Don't clear the favicon if this tab is in the pending
           // state, as SessionStore will have set the icon for us even
           // though we're pointed at an about:blank. Also don't clear it
+          // if the tab is in customize mode, to keep the one set by
+          // gCustomizeMode.setTab (bug 1551239). Also don't clear it
           // if onLocationChange was triggered by a pushState or a
           // replaceState (bug 550565) or a hash change (bug 408415).
           if (
             !this.mTab.hasAttribute("pending") &&
+            !this.mTab.hasAttribute("customizemode") &&
             aWebProgress.isLoadingDocument
           ) {
             // Removing the tab's image here causes flickering, wait until the
diff --git a/browser/components/customizableui/test/browser_reload_tab.js b/browser/components/customizableui/test/browser_reload_tab.js
index 6577984964cc..b12f5ee0e9b2 100644
--- a/browser/components/customizableui/test/browser_reload_tab.js
+++ b/browser/components/customizableui/test/browser_reload_tab.js
@@ -43,6 +43,11 @@ add_task(async function reload_tab() {
   gBrowser.reloadTab(customizeTab);
   await tabReloaded;
 
+  is(
+    gBrowser.getIcon(customizeTab),
+    "chrome://browser/skin/customize.svg",
+    "Tab should have customize icon"
+  );
   is(
     customizeTab.getAttribute("customizemode"),
     "true",
@@ -71,6 +76,11 @@ add_task(async function reload_tab() {
   await BrowserTestUtils.switchTab(gBrowser, customizeTab);
   await customizePromise;
 
+  is(
+    gBrowser.getIcon(customizeTab),
+    "chrome://browser/skin/customize.svg",
+    "Tab should still have customize icon"
+  );
   is(
     customizeTab.getAttribute("customizemode"),
     "true",