How to revoke given permission in Chrome and Firefox?

chrome://settings/content has a section that allows you to revoke location permissions.

For Firefox: Right-click the page, "View Page Info", there go to the "Permissions" tab. The entry you are interested in is "Share Location".

Edit (2016-05-12): In current Firefox versions you can also click the info icon next to the location bar. This will show you all the special permissions you've granted the current page and will allow changing them.

This approach works in Chrome as well, there you click the document icon next to the site name. Difference is that Chrome will show you a list of all permissions, not just the ones you've granted already.

In Android Chromium (default Android browser; usually called "Browser" or "Internet") you must go to Settings > Privacy > Remove private date, check Location access and click OK.

In Android Chrome open Menu (HW button or top-right button) and go to Settings > Advanced > Content settings > Website settings and uncheck Location access under each website you want to reset the settings.

For Android Firefox go to the page with location access and long press the URL bar (it have to be highlighted while you press it). In popup menu choose Edit site settings, check the Share location and click Clear.

And in Android Opera you must delete all web data (Menu > Settings > Clear Browsing data > Clear Cookies and Data).