Google Photos Cleaner by MyProjectsAreLovely

Google Photos Cleaner is an unofficial Firefox extension for managing large Google Photos libraries directly from photos.google.com.

It provides a compact on-page interface for:

moving one item or all enumerated Library/Archive items to Trash,
restoring one item or all enumerated items from Trash,
counting items in Library/Archive or Trash,
using the interface in English or Polish.

The extension does not automate Google Photos buttons or simulate mouse clicks. Operations are performed through the web RPC interface used by Google Photos itself.

For bulk operations, the extension asks for confirmation before scanning and starting the requested action.

Other Firefox extensions by this developer:
https://addons.mozilla.org/en-GB/firefox/user/19987152/

Privacy and safety

No analytics or telemetry.
No advertising.
No developer-operated server.
No third-party data transmission.
Google Photos session information and item identifiers are sent only to photos.google.com as required to perform the requested operation.
Session information and photo identifiers are not stored by the extension.
Only the selected interface language is stored locally.
The extension does not permanently empty Trash.
The extension does not operate on Locked Folder.

Important

Google Photos Cleaner is an independent, unofficial project. It is not affiliated with, endorsed by, or sponsored by Google.

The extension uses an undocumented Google Photos web RPC interface. Google may change this interface at any time, which can temporarily break some or all functionality.