how to install version 10

[jenniferdnn]

The latest add on version is 7, how can I install 10-unsigned version.
I got error from console, "HAR is not defined".

[jenniferdnn]

I installed 10 on firefox developer edition 55.0b14 (64-bit). Test the http://janodvarko.cz/har/tests/har-export-trigger/har-export-api.html, I still get har is not defined error.