Firefox validation on focus of an input checkbox (Angular 6)

In an Angular 6 app there is a component whose template is an extension of a simple labelled checkbox input:

<label>
  <input type="checkbox" required>
</label>

On Firefox 63.0.2 (mobile version), when the user clicks on the checkbox, for a fraction of a second the below popup appears:

I think this is the well-known Firefox feature of on-focus validation of input elements: the user clicks on the checkbox, the input is first focused and then selected, and in the interval between the two events the popup is displayed. I am confident this is the case as, if the required attribute is removed, the popup does not appear.

Has anyone got any idea how I can stop the popup from appearing? Most of the posts here related to Firefox on-focus validation focus on red border box and other styles which are easier to tackle, but I wonder if there is a way to stop that popup from appearing.