PageSigner

PageSigner - a cryptographically secure webpage screenshot toolPageSigner allows you to "notarize" web pages. Think of it as a cryptographically secure webpage screenshot - it's different from an ordinary screenshot in that it can't be edited in Photoshop; it really proves that you received that data from the server. You can then share that proof with anyone you like.
PageSigner is an open-source project. You can see the code here:
https://github.com/tlsnotary/pagesigner


October 2020 UPDATE:
Starting from version 2.0.0 PageSigner supports TLS 1.2. It uses a modified TLSNotary algorithm (not the one described in the TLSNotary whitepaper). Read more https://tlsnotary.org/wp/?p=45

Changelog.
v 2.1.0
- fix sending message to tab too soon before DOM is loaded (esp. on Vivaldi)
- allow to import older versions of notarization files
- more lightweight pgsg file format

v 2.0.1
- don't require management permission
- verify imported pgsg's certificates against the time of notarization