The intention is good, but the lack of a GitHub page so we can verify the code, and the fact that it actually slows down the sites a bit ruins it.

Der Webmail Ad Blocker verlangsamt den Browser. Für das was er kann ist das zu viel.

Cuando el complemento está activo en Firefox va alentando el nevegador mientras estoy checando o escribiendo correos. por ejemplo, me mandaron 10 fotos y al estar revisandolas llega el momento que el navegador está paralizado por tanto consumo de recursos. si desactivo el complemento todo va de maravilla.

this is not bad and it used to work efficiently in the past but ever since i switched to Yahoo!'s new email client interface last night, the 'Webmail Ad Blocker' started working erratically ...

for example, the left side panel's ad is gone totally but the top side and right side panels ads are still there, although the right side panel shows only one ad instead of two ...

some new updates / upgrades are due perhaps ...