This is a tweaked version of @rem’s awesome responsivepx tool (https://github.com/remy/responsivepx, live service at http://responsivepx.com).

Added features:

• Support for manual creation of predefined resolution values
  • Saved to localStorage, so they are preserved between page loads (note: doesn’t work in Firefox if loaded as a local file)
  • Switch easily between the saved presets using Ctrl+[LeftArrow|RightArrow]