I'm wondering if it because Okta is seeing it as Safari (without plugin installed, it prompts to install plugin = redirect to appstore version) so it must be something extension specific between the website and extension..
The requirement is Install Extension > Login to domain.okta.com > Extension then sync's and gets apps.
Tested;
User Agent: Default with Both Extensions = Not working
User Agent: Firefox with Firefox Okta Extension = Not working
User Agent: Chrome with Firefox Okta Extension = Not working
User Agent: Chrome with Chrome Okta Extension = Working