Tab Audio Recorder captures the audio playing in a browser tab and saves it locally, so you can build a sample library from anything that plays in Firefox. ONE BUTTON, THREE CAPTURE STRATEGIES The recorder tries three approaches in order, so the same Record button works across very different sites:

Media element - captures a playing audio/video element. It hooks play() in the page, so it also catches detached players (such as WhatsApp Web voice messages) and elements inside closed shadow roots.
Network stream - when there is no media element, a detected audio stream URL is fetched and recorded. This is what makes web radios work.
Web Audio - taps the page's own AudioContext for sites that synthesize sound instead of playing a file.

RECORD FROM THE VERY FIRST SAMPLE Press the button (or Alt+Shift+R) and it records immediately if audio is already playing. If nothing is playing yet, it arms the tab and starts the instant the next sound begins, so short clips are captured from the start. A toolbar badge shows the armed/recording state while the popup is closed. MANAGE AND EXPORT

Recordings manager with per-site filtering, sorting, an inline player, export and delete.
Export to WAV (lossless) or MP3 (smaller).
Filename templates, export subfolder, and optional auto-export.
Storage cap with automatic cleanup, bitrate and maximum recording length.

PRIVACY Recording happens only while you actively record a tab. Recordings and settings stay in your browser (IndexedDB and extension storage). Nothing is uploaded, transmitted, or shared with any server - the add-on declares no data collection. Exported files go to your own Downloads folder. LIMITATIONS

DRM/EME-protected playback (Netflix, Spotify web player, and similar) cannot be captured. Firefox yields a silent stream, so the add-on detects it and refuses up front instead of saving silence.
Long recordings are held in memory until stopped; use the "Max recording length" setting as a guard.

Open source (ISC): https://github.com/enzoomoreira/tab-audio-recorder