You can use multiple browsers to preview, I prefer to have it in the editor which makes it easier to switch between (same argument for code tabs vs windows). I still test and work in multiple browsers to ensure compatibility, but being able to get the rough parts laid out in the editor itself and fix/develop on things that are the same in all browsers is a great productivity boon (especially when i'm working on my laptop with limited screen real estate).
And again, I could run everything in a separate console window, logging to files, etc... But having that in the browser is a boon to my productivity. Having notifications in the browser window that a test that was running in the background failed and being able to click a button and open right to the test file + source file that failed along with annotations about coverage data in the sidebar saves me quite a lot of time and effort.
If Atom is useless for you, don't use it! But don't act like it's garbage for everyone. I don't need a car that goes 200MPH but that doesn't mean every F1 car is entirely useless, just that it's designed for a different purpose.
I currently have 3 different atom windows open, each with 1-4 panes with probably 5-20 tabs open in each and it's using a whopping 1.8GB (super rough counting, didn't want to actually add it all up). That's a lot, but it's not enough to outweigh the benefits for me. I'm not "sticking hardly to one regardless the pain", i'm sticking to the one which makes me the most productive and is the "nicest" for me to use (if i'm frusturated by constantly finding windows, i'm not going to be a better developer) It might be too slow/bloated/whatever for you, and that's okay, but for me it's more than fine.