In the search box in the page, type or paste compact and pause while the list is filtered.In a new tab, type or paste about:config in the address bar and press Enter/Return.Re-styling tab buttons as connected tabs, dividers, height, font size/boldness, audio icon, etc.Дo you miss having 'compact' toolbars? The developers have reduced support for Compact mode so if you would like to select it from the Density popup on the Customize screen, you need to change a preference so it appears there:.

Restoring Compact mode to the density selector.Here are some ideas for modifying these changes if they bother you, and of course you can find additional suggestions on the usual sites (especially r/FirefoxCSS). The feeling of spaciousness also extends to the menus. The design of the tab bar has been particularly controversial due to its greater height, and the way tabs float. Write about:profiles in the Firefox address bar and select Open Folder in correspondence of the 'Root Directory' of the user profile you want to customize (usually there's only one) Д«y now the profile's root folder should have opened, create (if it is not present yet) a new folder named chrome Д¬reate (if it is not present already) a new file named userContent.Before the 'Photon' user interface design reached its fourth anniversary, FirefoxВ 89 has brought us the 'Proton' user interface. You may decide you don't want to use an addon for this, well in this case here's what to do: So, let's leave addons aside and get our hands dirty! Each browser also restricts access to its ownД®xtensions gallery (like Chrome Web Store or AMO). Tab page as of Chrome 61, about:addons, and so on) as well as otherД®xtensions' pages. Stylus with Firefox 57's new tab page shows this message:ДЄs a security precaution, the browser prohibits extensions fromДЄffecting its built-in pages (like chrome://version, the standard new Neither of the above will work with Firefox 57 due to added restrictions.I think it's overkill if you only need it for the task we are dealing with here. Stylish is an add on with a broader spectrum of functionality it lets you customize Firefox itself as long as manage/install themes and skins for lots of popular websites such as Google, Facebook, YouTube and many others. This is a specific add on for the task, it not only let's you change the background color but also choose a background image and also resize and align it as you like. Customize about:newtab (please see point 3 below).So far I know a couple of addons to achieve that and a way to do without addons (as it seems a lot of them are disappearing day by day), here we go then: also, if you want, you can still juggle with CSS (see point 3 of original answer below). That said, if you're looking for something minimalistic there are also addons that work straight forward and provide just the very basic feature to only change the new tabs background to something dark, for example Dark New Tab or even Black New Tab. There are also some addons that, despite background, lets you customize tiles on new tabs as well, I think you may like it and find the thing useful so I'll provide some worth a try imho: Infinity New Tab (Pro), nightTab, New Tab Tools. (As a last note here let me say Tabliss is like joining the features of New Tab Override, New Tab Wallpaper, Beauty Tab, New Tab Splash and Clock New Tab addons all togheter.) It lets you customize the new tabs background not only choosing for a color but also beautiful background images and add widgets (like showing the time for instance). Tabliss This is a really nice one (I personally use and love it). If this isn't enough, let me add this addon is develope by Mozilla itself. I think this may interest others as well.Д«y now there's a lot of cool and interesting addons that do the job in great way, let me mention some of my favorite in a brief list:ДЇirefox Color This imho is really THE DEFINITIVE ONE and A MUST HAVE! Not only it lets you deeply customize almost everything of Firefox GUI the way you like it (including new tabs background of course), it also lets you share the theme you made if you want.

Firefox new tab background