Tut, was es soll.

works well

Cannot create a rule. Select "Create new rule" from extension's icon on the Toolbar ad some page flashes briefly then disappears.

I appreciate that someone ported this extension to firefox.

I have not yet tried it out properly, but wanted to post this script to compare the port-changes: https://gist.github.com/olejorgenb/a6c0a81e52a98a894f7f98a385ebd78b

I found it a bit suspicious that this was posted without any mention of where port lives. Unless the publisher is the author of the original extension he/her should not use the original extension as a homepage without any clarifications. Using the homepage make it look like it's an "official" port.