From: Yuttadhammo Bhikkhu
Message: 4521
Date: 2016-01-11
Dear Huynh Trong Khanh,
No doubt Venerable Yuttadhammo (the creator of this add-on) can provide more information on this, but for now here is how you can get it working:
1) In the location bar of Firefox, type "about:config" and press enter.
2) Search for "xpinstall.signatures.required".
3) Right click on this item and chose toggle. The "value" should now read "false".
DPR should now work. However, depending upon what other add-ons you have, according to Firefox there is a chance that the above process may allow malware and browser hijacking, so please proceed with caution!
Regards,
Chris