Hi, do you mean on random websites, you're invited to sign in to that site with your Google account? Or is it something else?

No, this pop up window just shows up on my home screen every now and then, asking me to sign into the old deleted gmail account I linked to thunderbird. It doesn't seem to be associated with any other website I am visiting or internet activity. It appears to me the prompt comes from Thunderbird asking me to log into my deleted gmail account so Thunderbird can import any emails contained in that gmail account.

If you removed that account from settings, I'm puzzled why Thunderbird would suggest signing in to it. Is it possibly still listed as an account that Thunderbird thinks it should be checking from time to time??

that was my thought as well. I searched every nook and cranny of the Thunderbird program and can't find anything associated with that old account.

Does the pop up say it is from Thunderbird? Is it a notification (from the Windows Action Center or whatever they call it now) or in some other format?

Good question and this is what's perplexing me. The pop up says to log into your gmail account, but it has a thunderbird logo on it. I've seen similar popups in the past when thunderbird can't access an external email account due to improper password e.g. , but this isn't the case. In addition, when I attempted to log in to this pop up, it never goes anywhere. Just sort of locks up. It hasn't reoccurred yet today so maybe it fixed itself.?? If it does show its ugly head, I'll try to get a screen shot and post it. Heck, it could be a phishing scam.