Current releases of the Mozilla Firefox webpage Browsers offers Page Size and Page View functions as follows:

Select the Tools drop-down menu, and Web Developer sub-menu; and click Responsive Design View

Select the size - if not custom, from 320 wide x 480 high to 1920 wide x 900 high. The Rotate button swaps width and height of size.

Internet Explorer 6 webpage Browsers and Internet Explorer 9 pinned site windows offer a Page Printer function as follows:

Select the File drop-down menu or Print sub-menu, and click Page Setup

Select the size - if not custom, from letter to A4. The sizes vary and are based on Printer selection.

Google Chrome webpage Browsers and others can offer Page Zoom function as follows:

Select the - or + to Zoom the page out and in from the intial 100%.