If you’re impatient, like me, you might agree that the worst part of making an online resource is testing the interface across devices and browsers. The golden rule that I tout is that all websites I make should look their best no matter how they are accessed: at any resolution, on any common mobile or desktop device, in all common browsers up to 7(ish) years old.
You can choose to own many devices (or virtual machines) and maintain a stable of old and new browser versions, which is tough but gives you the best taste of the user’s experience. Serious devs and tech companies usually have quite a collection of devices.
Your other option: you’ll have to rely on emulation software. My favorites:
BrowserStack — 60(?) minutes of free testing, then $19/mo for individuals thereafter. Test your URLs in a ton of browsers and in the most common desktop/mobile platforms. Their emulator is interactive, so you can click, scroll, and type.
NetRenderer — old reliable here. Test for free in IE 5.5–10. Paste in a URL and get a screenshot of how it looks on the screen, with the option to offset the screenshot by a number of pixels to peek past the fold.
What device/browser testing tools do you use?