Inspired by the 6 week release cycle of chrome, Firefox has also introduced THREE (main) release channels General, Beta, Aurora where General being the most stable (and thoroughly tested one). There is another channel called Nightly, where the features/changes are introduced and they gradually pop-up after usage/feedback/refinements. [ Details about Firefox main channels is available here: Firefox Channels ] The UX channels come under the nightly channel and the changes related to the user interface (or user experience) are pushed specifically in this channel.
The recent version of the Firefox UX channel has introduced some noticeable changes. These changes have been long in the pipeline in the proposed mock-up and now finally they are out here. Although small, the recent change give Firefox a fresh face lift.
The first one is the round corner tabs in-place of the old fashion, since day one, rectangular tabs. Similarly, the new tab button has also got rounded corners :
The more interesting is the download start animation. When a download link is pressed an animation is played. A downward arrow, similar to the download manager icon at the menu bar, appears in the center of the screen and and it fades out toward the download manager icon and turn it green. It is a unique (and stylish) way to inform user that the download has been started and its progress can be seen in the download manager.
Last but not the least, the old download timer is back. It shows the download time remaining. It was available in the some of previous releases. Once matured, it could be added to upper channels.