Sending, receiving, and organizing email in Outlook on the web for business
I'm getting this error when I click Install:
'Learn more' (not pictured - far right of that Chrome notification bar) takes me to a page which doesn't seem to cater to the exact issue here (below). I'm not experienced enough to know if one of those many options is the one to fix this - I'm just a guy who wants to use Outlook :)
You need to install the Tampermonkey extension first from the chrome web store. The script on greasyfork is for use within tampermonkey, it's not a chrome extension in its own right.
FYI tampermonkey is a way of putting your own code onto websites: here, the code we're asking it to run is just a few lines which override Outlook's behaviour around the option key. However in general, Tampermonkey can be very powerful and you should never install anything in it without being really, really sure it's what you want and that it comes from a trusted source.
Anyway, once the tampermonkey extension is installed, you can go back to the greasyfork link and click "Install script" and it will take you to the tampermonkey page for final confirmation. Or, if that fails, you can just copy/paste the script into a new tampermonkey script.