I can't sign into the Toolbar in Safari
In Sierra and earlier:
This is due to a bug in Safari's privacy handling. The solution for this is to go to Safari->Preferences, choose the "Privacy" tab and choose "Always Allow" in the "Cookies and website data" section (the default is "Allow from websites I visit").
Details of the problem:
Safari's default settings attempt to prevent 3rd party websites from tracking you by not allowing cookies/data from third party websites unless you've actually visited that website (which you presumably haven't for most advertisers). However, since you've been to scrible.com to sign up and to go to your library, the cookies/data should have been allowed for us, but there appears to be a bug in Safari which isn't allowing it.
In High Sierra:
Safari defaults to blocking all 3rd party cookies/data. The only work around is to allow those. To do this, go to Safari->Preferences, choose the "Privacy" tab and uncheck "Prevent cross-site tracking" in the "Website Tracking" section (defaults to checked). Also, ensure "Block all cookies" is unchecked (which is the default)
We realize this is not an ideal solution, but since Safari doesn't allow for site specific overrides, unfortunately this isn't something we have found a work around for. For our Toolbar to be able to know who you are and be able to securely communicate with your account when you load the toolbar in a 3rd party website (meaning a website with a host name in the address other than scrible.com), we need to utilize 3rd party cookies/local data storage.
As an alternative, Chrome and Firefox both allow you to disable 3rd party cookies, but have the ability to specify overrides to allow specific sites.
More details about 3rd party cookies and sign in issues can be found here.