--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -13128,17 +13128,23 @@ nsIDocument::UpdateStyleBackendType()
   mStyleBackendType = StyleBackendType::Gecko;
 
 #ifdef MOZ_STYLO
   if (nsLayoutUtils::StyloEnabled()) {
     if (!mDocumentContainer) {
       NS_WARNING("stylo: No docshell yet, assuming Gecko style system");
     } else if ((IsHTMLOrXHTML() || IsSVGDocument()) &&
                IsContentDocument()) {
-      mStyleBackendType = StyleBackendType::Servo;
+      // Disable stylo for about: pages other than about:blank, since
+      // they tend to use unsupported selectors like XUL tree pseudos.
+      bool isAbout = false;
+      mDocumentURI->SchemeIs("about", &isAbout);
+      if (!isAbout || NS_IsAboutBlank(mDocumentURI)) {
+        mStyleBackendType = StyleBackendType::Servo;
+      }
     }
   }
 #endif
 }
 
 /**
  * Helper function for |nsDocument::PrincipalFlashClassification|
  *