diff -u b/themekey_css/themekey_css.install b/themekey_css/themekey_css.install
--- b/themekey_css/themekey_css.install
+++ b/themekey_css/themekey_css.install
@@ -39,6 +39,17 @@
 }
 
 /**
+ * Implements hook_disable().
+ *
+ * We should delete 'themekey_css_debug_css_files' when module is disabled
+ * because if 'themekey_css_debug_css_files' == TRUE but module was disabled
+ * there will be css debug message on a page.
+ */
+function themekey_css_disable() {
+  variable_del('themekey_css_debug_css_files');
+}
+
+/**
  * Implements hook_uninstall().
  */
 function themekey_css_uninstall() {
diff -u b/themekey_css/themekey_css.module b/themekey_css/themekey_css.module
--- b/themekey_css/themekey_css.module
+++ b/themekey_css/themekey_css.module
@@ -121,0 +122,14 @@
+
+/**
+ * Implements hook_form_alter().
+ *
+ * Add 'Show list of css files' option on debug settings form.
+ */
+function themekey_css_form_themekey_debug_settings_form_alter(array &$form, array &$form_state, $form_id) {
+  $form['themekey_debug']['themekey_css_debug_css_files'] = array(
+    '#type' => 'checkbox',
+    '#title' => t('Show list of css files'),
+    '#default_value' => variable_get('themekey_css_debug_css_files', FALSE),
+    '#description' => t('Prints out detailed information about css files added on a page. Useful to debug ThemeKey Css rules.'),
+  );
+}
diff -u b/themekey_css/themekey_css_admin.inc b/themekey_css/themekey_css_admin.inc
--- b/themekey_css/themekey_css_admin.inc
+++ b/themekey_css/themekey_css_admin.inc
@@ -32,11 +32,10 @@
     'CSS_SYSTEM' => 'system',
   );
 
-  $css_weight_options = array();
-
-  for ($i = -50; $i <= 50; $i++) {
-    $css_weight_options[$i] = $i;
-  }
+  // range(-50, 50) returns array with keys from 0 to 100
+  // but we need array with keys from -50 to 50
+  // because keys will be values for select.
+  $css_weight_options = drupal_map_assoc(range(-50, 50));
 
   return themekey_abstract_rule_chain_form($form, $form_state, array(
     'load_rules_callback' => 'themekey_css_load_rules',
diff -u b/themekey_debug.module b/themekey_debug.module
--- b/themekey_debug.module
+++ b/themekey_debug.module
@@ -171,14 +171,9 @@
     themekey_debug_properties();
   }
 
-  if (variable_get('themekey_debug_show_css_files', FALSE)) {
+  if (variable_get('themekey_css_debug_css_files', FALSE)) {
     // add the list of css files to the end of debug messages.
     $list['title'] = t('Css files on a page');
-    // drupal_get_css() returns html markup with "@import" statements combined in <style> tags.
-    // themekey_set_debug_message() use filter_xss() to filtering html from string, but filter_xss() leaves
-    // empty string where was html markup.
-    // So we should filter elements that contains <style> tag
-    // in exploded array with themekey_debug_filter_css_array() function.
     $list['items'] = array_filter(explode("\n", drupal_get_css()), 'themekey_debug_filter_css_array');
     themekey_set_debug_message(theme('item_list', $list));
   }
@@ -199,6 +194,11 @@
 /**
  * Function for filtering array elements.
  *
+ * Filters elements with empty strings and elements with strings that contains '<style>' tag from array
+ * generated by explode("\n", drupal_get_css()). drupal_get_css() returns html markup with "@import" statements
+ * combined in <style> tags. themekey_set_debug_message() use filter_xss() to filtering html from string, but
+ * filter_xss() leaves empty string where was html markup.
+ *
  * @param string $element
  *   Array element.
  *
reverted:
--- b/themekey_debug_admin.inc
+++ a/themekey_debug_admin.inc
@@ -39,13 +39,6 @@
     '#description' => t('Prints out detailed information about matching or non-matching rules.'),
   );
 
-  $form['themekey_debug']['themekey_debug_show_css_files'] = array(
-    '#type' => 'checkbox',
-    '#title' => t('Show list of css files'),
-    '#default_value' => variable_get('themekey_debug_show_css_files', FALSE),
-    '#description' => t('Prints out detailed information about css files added on a page. Useful to debug ThemeKey Css rules.'),
-  );
-
   $form['themekey_debug']['themekey_debug_non_admin_users'] = array(
     '#type' => 'checkbox',
     '#title' => t('Show debug information to all users'),