0. Know your email address
Well, it sounds logical
1. Compose and send new mail.
Looks reasonable once we would like to compose and to send signed / encrypted S/MIME messages.
2. View, manage and permanently delete your mail in Gmail.
View also looks normal since we gonna view S/MIME messages. Manage and delete sounds rather intriguing but it let us create and keep a single copy of encrypted S/MIME message in your Sent box when you send it to several recipients. It is your personal copy you can view when in fact each your recipient has got a copy encrypted specifically for him.
3. Create, update and delete labels.
For your convenience, we create (if not exists) S/MIME label and mark S/MIME messages by it.
4. View your settings (e.g. filters and labels).
Helps us to check if you already have S/MIME label or not.
5. Read and change all your data on the websites you visit.
This is #1 reason for questioning us. The reason Fossa Guard requires this permission is the necessity to download Certificate Revocation List (CRL) from URLs discovered in your certificates. Fossa CRL is accessible at https://fossa.me/crl/f2.crl by the way. Certification validation vs actual CRL is a mandatory check according to the specification and it was introduced since V0.2.1.
One can also understand it as also the permission to read browser history, but it's not actually it. There is an interesting and sometimes funny discussion about the right sentence for the last permission.