I was having the same problem as several others on the forum, that Thunderbird was freezing up a lot after I updated to Windows 10, so I (probably stupidly) just downloaded the Thunderbird version for Windows 10 and made it my default mail program as usual. I can see all of my various e-mail accounts in my account settings, my Address Book is there, and I can write e-mails on my Gmail account. But I can't get into the old view where my accounts were all listed on the left sidebar and when I click on "read messages" in my Gmail account, nothing happens. I've tried every view there is, I've tried to open all the folders. I've also discovered that although I can write FROM my Gmail account to my own domain account, I can't do the opposite. Also the e-mails I write can't be copied to my "Sent Mail" or "Drafts" folder. What do I need to do?