So, I'm trying to test out an app in our org's sandbox; I click 'get it now', it tells me I need to log in. Okay, makes sense, but then I get this: 


Closing the 'login successful' window punts the dialog box back to the 'please log in' screen.
This also happens in the production org, and with other apps; have pulled up the browser dev console and see two warnings (first one visible in the screenshot), but have not yet acted on them. 
Have successfully downloaded+installed apps from the AppExchange before, but not since July or so.
Am I doing something wrong here, will clearing the browser cache work, or is it something on Salesforce's end?

So, I'm trying to test out an app in our org's sandbox; I click 'get it now', it tells me I need to log in. Okay, makes sense, but then I get this: 


Closing the 'login successful' window punts the dialog box back to the 'please log in' screen.
This also happens in the production org, and with other apps; have pulled up the browser dev console and see two warnings (first one visible in the screenshot), but have not yet acted on them. 
Have successfully downloaded+installed apps from the AppExchange before, but not since July or so.
Am I doing something wrong here, will clearing the browser cache work, or is it something on Salesforce's end?