Existing users will be automatically updated. If you’ve opted out of auto-update or just want to try out the latest version of Firefox, head on over to the Mozilla downloads page.
Web developers get a few new features to test in this release, including support for more of WebRTC and the latest CSS 3 Flexible Box Model syntax. The latter is still disabled by default. To enable it open up
about:config and search for “flexbox.”
Another welcome, but disabled-by-default feature is a setting to stop insecure content from loading on secure websites. Turning it on may break a lot of sites (mixing HTTP and HTTPS content on the same page is, sadly, quite common), but it will make your browsing more secure. Head to
about:config and search for “mixed,” which will bring up the relevant options.
For more details on everything that’s new in Firefox 18 — including a new HTML scaling algorithm that promises to make images sharper — be sure to read through Mozilla’s release notes.