As per comment #20 and https://github.com/kewisch/gdata-provider/issues/26#issuecomment-547994463, setting general.useragent.compatMode.firefox to true allows IMAP access again. Not tested for gData, but no reason to distrust the GitHub post.
As per comment #20 and https:/ /github. com/kewisch/ gdata-provider/ issues/ 26#issuecomment -547994463, setting general. useragent. compatMode. firefox to true allows IMAP access again. Not tested for gData, but no reason to distrust the GitHub post.