Disable link dragging and select text.
< Select text inside a link like Operaについてのフィードバック
Maybe it's the problem of Violentmonkey. Can you post the URL that the script doesn't work on?
BTW, currently there are many issues with Violentmonkey on Firefox e.g. script would be blocked by adblock addon, doesn't work on CSP restricted page. I would suggest you to use Tampermonkey instead.
unluckily very ureliable
very unreliable(it often wont work) with firefox 58 and violent monkey on mac osx please fix it