ProtonMail (unofficial) by Mailueberfalln

Unofficial ProtonMail extension. Provides notifications and/or unread count badge.
Issues and help: https://github.com/gitladen7/protonmail-webextension/wiki
Source code: https://github.com/gitladen7/protonmail-webextension

General Settings:
Fetch interval: Select how often the extension will check for new emails.

Settings:
Persist session: Check it to keep the sessions in browser memory.
Persist session even if browser is closed: Check it to save the sessions to disk. WARNING: Your mailbox password will be written to your hard drive.
Show unread count badge: A badge will show on the extension icon with the number of unread emails on the INBOX.
Show notifications on new emails: If checked then the extension will show a notification when you receive an email.
Enable peeking: If checked then you will be able to see a list of your inbox unread emails in the extension itself.