--- a/dom/media/gmp/GMPServiceParent.cpp
+++ b/dom/media/gmp/GMPServiceParent.cpp
@@ -1056,16 +1056,23 @@ GeckoMediaPluginServiceParent::RemoveOnG
     MutexAutoUnlock unlock(mMutex);
     for (auto& gmp : deadPlugins) {
       gmp->AbortAsyncShutdown();
       gmp->CloseActive(true);
     }
   }
 
   if (aDeleteFromDisk && !inUse) {
+    // Ensure the GMP dir and all files in it are writable, so we have
+    // permission to delete them.
+    directory->SetPermissions(0700);
+    DirectoryEnumerator iter(directory, DirectoryEnumerator::FilesAndDirs);
+    for (nsCOMPtr<nsIFile> dirEntry; (dirEntry = iter.Next()) != nullptr;) {
+      dirEntry->SetPermissions(0700);
+    }
     if (NS_SUCCEEDED(directory->Remove(true))) {
       mPluginsWaitingForDeletion.RemoveElement(aDirectory);
       NS_DispatchToMainThread(new NotifyObserversTask("gmp-directory-deleted",
                                                       nsString(aDirectory)),
                               NS_DISPATCH_NORMAL);
     }
   }
 }