for some reason, the firefox extension is out of date by two years. the latest update is of may on github, though there's been reports where if you do fetch the newest version of the firefox extension via the github, it's corrupted allegedly. i've had luck though with the tampermonkey script which installs easily if you have the tampermonkey extension.
whether it's because mozilla is taking a long time to approve the newest version of the extension or the extension developer hasn't updated it yet here due to unknown reasons, just go with the tampermonkey script. it does the job and it works!