Old problem comes back due to different reasons. Firefox follows chrome and drops support for NPAPI plugins (it affects Silverlight and Flash as well).
By default support is disabled, but you can revert in.
- Go to about:config settings webpage (type it as uri in browser and press enter)
- Add new entry of boolean type with name plugin.load_flash_only and value set to false
- Restart browser and your java and silverlight should work again!