Mozilla has released Firefox 19, which features a few modest improvements including a built-in PDF viewer, faster startup times and support for some new web standards.

Firefox users will be automatically updated to the latest version. If you’d like to take Firefox for a spin, head on over to the downloads page.

The biggest news in Firefox 19 is the new, baked-in PDF viewer based on PDF.js. It may not mean the end of those annoying (and untrue) buttons that say “you need Adobe Acrobat to view this file,” but at least you don’t, well, need Acrobat just to view a PDF.

This release will also be a welcome update for anyone who’s ever double-clicked on Firefox, seen nothing happen, double-clicked again and so on until Firefox suddenly comes to life with twenty blank pages open. As of Firefox 19, the browser will not execute any code before the initial window is made visible, which means you click Firefox and you see an open window much faster.

While there are not many new features in Firefox 19, web developers do get some love with support for several new CSS features, including @page, full width text transforms and the new viewport percentage units like vh, vw, vmax and vmin — handy for sizing elements or adjusting type based on viewport size. Just don’t try to use vh and the like with @page because the W3C still hasn’t quite settled how that will work.

For a full list of all the other smaller changes and bug fixes in Firefox 19, check out Mozilla’s release notes.

To help protect users from outdated, compromised third-party plugins like Adobe Flash, Microsoft Silverlight and Java, Firefox will stop automatically loading third-party plugins.

The only exception is the current Adobe Flash plugin.

Provided you’ve been keeping the Flash plugin updated, you may not even notice the change. But if you’re running an older, vulnerable version, video on sites like YouTube will no longer automatically load movies. Instead you’ll soon see a gray box and notice warning you that your plugin is out of date.

Michael Coates, Mozilla’s Director of Security Assurance, cites crashes as the main motivation for the change. “Poorly designed third-party plugins are the number one cause of crashes in Firefox,” writes Coates on the Firefox blog. “By only activating plugins that the user desires to load, we’re helping eliminate pauses, crashes and other consequences of unwanted plugins.”

Third-party plugins are also a notoriously popular way to deliver viruses and other malware.

Of course the click-to-play option can’t protect you from yourself – all you need to do to make the plugin in question run is click on the grayed out box and everything will work as usual. There’s also a new plugin icon in the URL bar; click it and a menu will show you which plugins on the page are disabled. Click “activate” to enable them, though obviously it’s a better idea to update Flash to the latest version.

One of the most common uses of Flash on the web these days is to deliver video to web browsers that don’t support the popular H.264 codec. When Firefox’s native support for H.264 video and MP3 audio arrives later this year, most Firefox users will likely have considerably less need for the Flash plugin.