Problem with installing a Safari extension

[A.Chakery]

Hello,

I am trying to install a Safari extension (this plugin) but when I double click on the downloaded file Safari says that this is not trusted and when I click on the TRUST button , nothing happens.


Would you please help me regarding this issue ?


Thank you very much.

 

[A.Chakery]

Any replies ? I am in a really bad situation .. please help