It is a little annoying to change screen properties to see how your site functions at different resolutions. It is especially annoying when you are designing.
I have been using something that actually makes it easy to view your web pages at any resolution without having to actually change any settings on your computer.
It is from Pythoness Software and it is called Size-O-Matic. Best of all, it is free. But you can make a donation if you want, however it isn't required.
I like Size-O-Matic. I know a couple other people who use it and they feel the same about it as I do. So I thought I would mention it in case some of you might want to give it a try and see if it serves your needs.
Here is a link where you can obtain additional information as well as download Size-O-Matic and give it a try
Pythoness Software: Home of Size-O-Matic