I'm coding html for ebooks, and my first test is in the Firefox browser. I need a down-and-dirty to simulate and compare web design in different device viewports in both landscape and portrait mode.
When I use the web developer --> responsive design view in Firefox, I have some presets, and if I click the rotate button I can see both landscape and portrait mode. But I don't see any capability to add custom viewport dimensions... which is strange given all the devices which are coming out these days.
Is there a way to do this? Also, is there a good URL which lists all the most popular viewport sizes for devices?