Clipboard Modifier by Mitch Crane

Clipboard Modifier is a Firefox add-on that lets you define regex-based rules to automatically rewrite copied text.

When you copy selected text from a webpage, the add-on can transform it before it reaches the clipboard, using rules you create in the popup. It also watches for browser-level copy actions, such as copying from the URL bar, so the same rules can be applied there too. Rules can be enabled, disabled, reordered, edited, and deleted, and the polling interval for browser-UI copy detection is configurable.

Typical uses include stripping tracking parameters from URLs, replacing repeated text patterns, cleaning copied content, or reformatting text as you copy it. Example: one might use it to change facebook links to facebed so that previews work in Discord.