The search query typically refers to browser extensions or add-ons that claim to let you download YouTube audio as MP3 files directly within Mozilla Firefox.
Instead of searching for a Firefox extension that may disappear or harm your browser, use: mp3 downloader youtube firefox
While more complex, this tool is the "Swiss Army Knife" of video downloading. It detects media on almost any site, including YouTube, and allows you to "Download & Convert" the audio stream into a local MP3 file. The search query typically refers to browser extensions
While this is not a Firefox extension, it is what most former extension users switch to. While this is not a Firefox extension, it
If you still want a Firefox extension, search the add-on store for – it's one of the few legitimate tools (though it often requires an external companion app for MP3 conversion).