diff --git a/lib/editor/tinymce/lib.php b/lib/editor/tinymce/lib.php
index a91c8a76473..b3479c027af 100644
--- a/lib/editor/tinymce/lib.php
+++ b/lib/editor/tinymce/lib.php
@@ -156,6 +156,7 @@ class tinymce_texteditor extends texteditor {
                 'searchreplace,paste,directionality,fullscreen,nonbreaking,contextmenu,' .
                 'insertdatetime,save,iespell,preview,print,noneditable,visualchars,' .
                 'xhtmlxtras,template,pagebreak',
+            'gecko_spellcheck' => true,
             'theme_advanced_font_sizes' => "1,2,3,4,5,6,7",
             'theme_advanced_layout_manager' => "SimpleLayout",
             'theme_advanced_toolbar_align' => "left",
diff --git a/lib/editor/tinymce/plugins/spellchecker/lib.php b/lib/editor/tinymce/plugins/spellchecker/lib.php
index b2aee6d4bff..b4f51180013 100644
--- a/lib/editor/tinymce/plugins/spellchecker/lib.php
+++ b/lib/editor/tinymce/plugins/spellchecker/lib.php
@@ -35,6 +35,9 @@ class tinymce_spellchecker extends editor_tinymce_plugin {
         // Check at least one language is supported.
         $spelllanguagelist = $this->get_config('spelllanguagelist', '');
         if ($spelllanguagelist !== '') {
+            // Prevent the built-in spell checker in Firefox, Safari and other sane browsers.
+            unset($params['gecko_spellcheck']);
+
             // Add button after code button in advancedbuttons3.
             $added = $this->add_button_after($params, 3, 'spellchecker', 'code', false);