Hi, Brian
I'm able to add Dropbox in Chrome on the Mac, no problem. However, I do see an issue with Safari. (I don't get a blank window..I get no window at all.).
For Google Drive, does your Google account have that wonderfully-named exception "Allow Less Secure Apps" enabled? Are you using 2-step verification on your account?
Derek Curtis
COO
SmarterTools Inc.
www.smartertools.com