Added support for "https://statics.teams.cdn.office.net/evergreen-assets/safelinks/2/atp-safelinks.html"

Due to issues with the changes that have been introduced with 1.7.0 (see GitHub issues),
I have decided to revert the corresponding changes for now, as our privacy
is more important than the features that have been added.

If you have experience with Firefox Add-On development (and especially Manifest V3 and
background scripts), please do not hesitate to reach out and help on GitHub.

Thanks in advance, and sorry for any inconvenience!

- Added "allow list" option for limitting the add-on to user-configured URLs
- Upgrade to Manifest v3

Thanks to @LukeCz for the contributions!

Add support for office365.us Safe Link domains (e.g. "usg01.safelinks.protection.office365.us") (#8).

Added support for regional Safe Link domains (e.g. "eur01.safelinks.protection.outlook.com")

This version of the add-on drastically reduces the amount of access that the code has, since it limits the execution of the add-on to only those sites that actually _are_ Safe Links redirect pages.

In addition, the code for preparing the redirect is much cleaner and easier to maintain.

Thanks a lot to @LukeCZ on GitHub for your contributions!

This version adds an icon for the Add-on.

Add support for new Safe Links in Microsoft Teams (https://statics.teams.cdn.office.net/evergreen-assets/safelinks/1/atp-safelinks.html?url=...)

Credit: @mpexo