Step 1
Go to Outlook Web, Manage Add-ins:
https://outlook.office.com/?path=/options/manageapps
or
https://outlook.office365.us/?path=/options/manageapps
(if your account is in Office 365 USGov)
Step 2
Select My add-ins
Step 3
Scroll to Custom add-ins and choose Add From URL...
Step 4
Enter URL
https://freebusy.io/outlook/officestore.xml
Click Ok, accept the warning and then click Install
Note: If you receive an error about not being able to open the URL, open the URL yourself in your browser, save it as a .xml file on your desktop and use Add from file... to pick the file your saved on your desktop
Step 5 - Outlook desktop
When you compose or reply to an email in Outlook desktop and when you schedule or reschedule a meeting in Outlook desktop, you'll be able to open the FreeBusy add-in from the ribbon (aka command bar).
Step 5 - Outlook Web
When you compose or reply to an email in Outlook web you'll be able to open the FreeBusy add-in from the lower toolbar (might be necessary to search it in the drop-down menu).
When you schedule or reschedule a meeting in Outlook web, you'll be able to open the FreeBusy add-in from the upper toolbar in the event editing extended dialog:
