When the pop up appears, do you also click on: "Download should start, you can also Download subtitles manually
If so, that's why it's downloading twice. Don't click on that pop-up and it should download just once.
I'm not experiencing that problem on Chrome. As you're only experiencing that problem on Chrome and not on FF, why not just use FF? As the problem seems to be from your end and your settings in Chrome and not a problem from opensubtitles (OS) side, don't really know how to help, except to recommend playing around with settings in Chrome. Most admins I know have stopped using Chrome, too.
You could try:1
: ABP instead of UBlock in Chrome and see if that changes things.2
: Just use FF for OS needs.3
: If you want to keep using Chrome, instead of clicking on the download button, click on the filename instead. That shouldn't launch any pop-up and should download the .srt straight to your download folder without the .zip file.
Check following post for picture instructions: viewtopic.php?t=16695#p41159
Hope that helps.