Firefox has already uploaded Firefox 20 to their servers, although the official release is yet to come; it will arrive later today. The new release brings to the table important modifications that improve the file download experience and per-window private browsing.
Firefox 20 includes the new panel-based download manager that has been announced in the beta revision. The component is now integrated in the browser interface, showing the job progress and details right next to the search bar.
Starting this revision, Mozilla’s browser features per-window private browsing, which allows you to start a new private session in a new window. In previous builds, navigating in private mode involved temporarily giving up the regular session. Now you can work with both the private and the regular one at the same time.
Additional improvements that should make it to this release are alerts about plugins hanging and the possibility to restart them (without the browser), as well as informing the user that the search engine has been changed (either by third-party software or from about:config panel) and offering to reset to the default choice.