Connection failure while downloading addon for some user

I have hosted an unlisted version of an addon here. This is signed build and working fine for me but for some other user he is facing a connection failure issue.

Here is the screenshot:

Any help would be appreciated.

Browser info: Firefox v52 on windows 7

It works for me, so there may be some temporary server issue. If there are users still experiencing the problem, maybe you can get them to open the Browser Console and see if there are any errors reported in it.

Thanks @jorgev. Actual Issue was presence of anti virus software which was causing this issue. After that particular user disabled his ESET NOD32, he was able to install the addon.

I am wondering why anivirus is blocking such installation.