How do I remove URL specific settings?
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If one URL specific setting is set for a URL it shows up at every setting that can have URL specific values. So if you click on the little "x" to reset the value the line for the URL may not disappear. But the input field will appear a little bit gray to indicate that the "normal" value is still used for this URL.

To get rid of this URL line you have to remove all specific settings for this URL. The easiest way to get to know which settings are still set you can go to General > Settings > Export settings > Inspect. There the entry "urlSettings" stores the url specific values.