Cookie Manager by Rob W

More detailed documentation at: https://github.com/Rob--W/cookie-manager#readme

By default, the Cookie Manager opens when the extension starts up. This allows you to keep the extension disabled until you need it.

You can also turn off the automatic opening, and manually open the cookie manager by clicking on the extension button in the toolbar (desktop) or the Cookie Manager menu item.

Supported features:

• Viewing all cookies
• Querying cookies by any combination of url, domain, path, cookie content (name/value), httpOnly/secure/sameSite/session flags, expiration time range.
• Recognizes cookie jars (default, private browsing mode, container tabs aka userContext).
• Allows you to remove individual cookies, or all matching cookies with one click.
• Supports Firefox for Android (Fennec)
• Supports the TOR Browser (and first-party domain cookies)
• Add cookies
• Edit cookies
• Import / export cookies
  
  • JSON format for backup and restoration purposes.
    
  • Netscape HTTP Cookie File format for use with other tools like curl and wget.
• Whitelisting cookies

There are lots of bugs in Firefox around private browsing cookies, with the majority being fixed in Firefox 58. The extension attempts to work around every bug where possible. For details, see https://github.com/Rob--W/cookie-manager#browser-specific-notes
The bug that affects most users is that in Firefox 55 and earlier, private browsing cookies can only be set when the cookie manager is opened from a private browsing tab. If you try to edit a private browsing cookie of a site on the Tracking protection blocklist, then you must temporarily disable Tracking protection, via the "Tracking protection" checkbox at Settings > Privacy.