Gmelius is a cross-browser extension that proposes a better and cleaner Gmail™ inbox. Gmelius gives you the possibility (i.e. option) to remove all the ads present in Gmail (top, right and bottom). And Gmelius offers to remove people widget, customize navigation icons, attachment icons (for more than 40 types of files) and more features to your Gmail interface.
Gmelius currently supports Chrome, Firefox and Opera. After you installed this extension to your browser just open the option page and select which feature you want and hit the save settings button on below.
Finally refresh your Gmail page and see the changes you have selected on Gmelius.