Use the following steps to manage and uninstall Orkut themes in Firefox:
Managing Orkut Themes
Right-click on the monkey icon in the status bar (bottom right side) of Firefox browser. Click on ‘Manage User Scripts’. The ‘Manage User Scripts’ dialog box opens up in which you can rearrange the sequence of your themes by dragging-and-dropping with the mouse. The theme which is last in the list will be the default theme that will be shown on your Orkut page. After rearranging the themes do not forget to refresh your Orkut page, otherwise the new theme will not be shown.
Uninstalling Orkut Themes
Select the Orkut theme that you want to uninstall and click on the ‘Uninstall’ button and that theme will be uninstalled. Refresh your Orkut page so that the previous theme (or default theme) is shown.