Photon is a new design that creates a fluid, native experience on every operating system. There is more room above the tabs, the search bar and address bar now have the option to be combined or separated, and the menus in Firefox are organized by common tasks.
In order to customize all your favorite functions, you can use the ‘Customize’ setting in this new menu. See the Customize Firefox controls, buttons and toolbars article for more info.
Where is the Downloads button?
The Downloads button is not shown by default, but will appear when you download a file from the web. If you want to permanently add it to the toolbar, follow the steps in this article to find and add it to the toolbar.
How can I reorder my New Tab Preferences (about:newtab)?
Currently you cannot change the layout of the new tab page, but I recommend having a look at the addons.mozilla.org website where you may find an add-on that will help you customize that page.