Download Link: https://addons.mozilla.org/firefox/addon/ui-text-overrider/

Provides ability to override UI elements' label, tooltip text, etc.

If you define some preferences like following, this addon automatically apply new labels, tooltip texts, and so on.

user_pref("[email protected]",             "CSS selector for the element");
user_pref("[email protected]",       "new label");
user_pref("[email protected]", "new tooltiptext");
user_pref("[email protected]",   "accesskey");

user_pref("[email protected]",             "CSS selector for the element 2");
user_pref("[email protected]",       "new label2");
user_pref("[email protected]", "new tooltiptext2");
user_pref("[email protected]",   "accesskey2");
// If the item is automatically inserted by another addon,
// then you should set this "delayed" flag to override labels certainly.
user_pref("[email protected]",     true);

...

For example, following preferences will change the label of "Firefox" button to "Iceweasel".

user_pref("[email protected]",       "#appmenu-button");
user_pref("[email protected]", "Iceweasel");

The value of the base key is always a CSS selector string to find the target element. You can specify any attribute name and value as child keys.

Note: original attribute and values won't be restored even if the addon is disabled or uninstalled, until you restart Firefox.