Near the top of my most-used resources is Can I use…, an incredible resource that shows you if a particular web technology is supported in the browsers you care about. It contains a wealth of information about browser support for HTML, CSS, JavaScript, SVG, Security, and more.

Just visit the site, type something in the text field at the top, and out pops some incredibly useful information tables. You can tell at a glance which versions of which browsers support what you've searched for, including full, partial, or no support. The tables can be adjusted to show various factors like global or regional market share, relative usage, browser release date, and more. You even get notes, known issues, and resources at the bottom of each result.