Prevent Tab Closing

Seems to work fine once I clicked on Enable and typed in the URL to lock. Not exactly intuitive but it does exactly what I want so thanks for making it available!

Did not work for me

Either this extension doesn't work at all, or its UI is so unintuitive that I don't know how to use it. It's unclear whether the regex is required, or if a blank regex is as good as '.*'. It's also unclear whether the extension has accepted, or is acting upon, the input expression. The 'save' button is gray, implying that there are unmet conditions for entering the expression, and when you click it, the value entered doesn't go anywhere. Whether enabling with no expression, entering an expression of '.*', or writing an expression to explicity match a certain URL, the extension has not warned me before closing the tab.