The update includes a big change with a new built-in PDF viewer. This removes reliance on the Adobe PDF plug-in and allows you to open and read PDFs right in the browser. Firefox 19 now supports the same in-browser PDF function as Google Chrome and Apple Safari.
Other changes include startup performance improvements, HTML5 changes, and more developer options. Another important change is that Firefox will offer to reset the “Awesomebar” or URL bar for the default search provider if it has been automatically changed by a software installer.
The other update was for Firefox Beta on Android. The update didn’t add any big internal improvements except support for themes. Firefox Beta’s big change was adding device support by lowering device CPU requirements from 800MHz to 600MHz. This will allow Mozilla to test the browser on a wider range of devices.
The updates to Firefox 19 and Firefox Beta aren’t huge leaps forward, but they add improvements and usability that will eventually make it into the stable release of Firefox.