My e-mail stopped working a week ago. I get to "connecting to IMAP but then get a "Sign-in failed" message

You should first verify that your server settings are correct. I can't find and official Orange.fr help page for this, but I found some other sources that may or may not be accurate. From what I can find, the settings might be: IMAP configuration details include: IMAP Server: imap.orange.fr Port number: 993 Authentication method: Normal password Email encryption: SSL/TLS mandatory POP3 Server: pop.orange.fr Port 995 with SSL/TLS enabled Authentication: normal password SMTP server: smtp.orange.fr Port numbers: 465 (SSL) or 587 (TLS) Mandatory authentication with valid Orange credentials Support for STARTTLS to enhance security This source says that the servers can authenticate by either Normal Password or OAuth2. Thunderbird's setup wizard doesn't seem to know about OAuth2 in this case, so take that with a grain of salt. How are you set up to authenticate? Some email providers require that you generate an "app password" in order to use third-party email programs like Thunderbird. I see some talk suggesting that Orange may be one of those, but I find no official confirmation of that. If you use OAuth2, app passwords are not used. What I'm saying is that you may have to contact Orange to find out the correct email settings and to ask if an app password is required. It may help for you to remove any existing passwords from Thunderbird's Saved Passwords (see <Settings | Privacy & Security | Passwords | Saved Passwords>), after which you will be prompted again for your credentials next time you fetch or send email.