I reloaded the thread, reopened the browser and rebooted my PC, but it still doesn't work.

Not only does this not work it installs a service worker.

Does not work

Do not use.

This extension can't download webms, only jpegs and gifs. Personally I hate the webm format but sadly it's 90% of what 4chan uses nowadays.

[Sorry I have to change my review because this is important stuff.]

Should you use "4Chan Media Downloader" in Private Browsing Mode, the files you download with it will actually appear in the Downloads of the Normal Mode. This is quite a big issue!

Yeah clicking the icon does nothing.

j'ai bien l’icône qui s'affiche dans firefox mais quand je clique dessus cela ne télécharge pas les images 4chan