Ytdyklly

I always use dark personas theme or the default compact dark theme that comes included with Firefox and I don't like the default background color being white when I open a new tab.
There was an add on I used that let me customize new tabs but it's gone now with Firefox 57...

So, how can I do to change new tabs background?

I think this may interest others as well.
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:

1. 
   

   Customize about:newtab (please see point 3 below)

   
   
   

   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... nice!

   
   


2. 
   

   Stylish (please see point 3 below)

   
   
   

   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... I think it's overkill if you only need it for the task we are dealing with here.

   
   


3. 
   

   Neither of the above will work with Firefox 57 due to added restrictions. Stylus with Firefox 57's new tab page shows this message:

   
   
   

   
   

   As a security precaution, the browser prohibits extensions from
   affecting its built-in pages (like chrome://version, the standard new
   tab page as of Chrome 61, about:addons, and so on) as well as other
   extensions' pages. Each browser also restricts access to its own
   extensions gallery (like Chrome Web Store or AMO).

   
   

   
   
   

   So, let's leave addons aside and get our hands dirty!

   
   
   

   You may decide you don't want to use an addon for this, well in this case here's what to do:

   
   
   
   
   

   • 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);

   
   

   • by now the profile's root folder should have opened, create (if it is not present yet) a new folder named chrome;

   
   
   • 
     

     create (if it is not present already) a new file named userContent.css
     inside the chrome folder and put the following code in it:

     
     
     

     @-moz-document url("about:newtab") {  
     
         body {
     
             background-color: #000000 !important;
     
         }
     
     }
     
     

     
     
   
   
   
   

   If you can juggle with CSS, you may also add some code to set a background image if you like (I suggest to eventually put the images in the same folder with the CSS).

   
   
   

   You may need to restart Firefox to make customization being applied.

   
   
   

   Credits for this last point goes to DIENER_

   
   

Well, I must say the solution given by @danicotra does work for new tab, even with Firefox 57. However, during loading of a page, a blank flash will still systematically burn your eyes.

Here is an other proposal of content for your ~/.mozilla/firefox/xxxxxxxx.default/chrome/userContent.css, which does darken a few more places, but won't resolve the blank flash on load.

/* https://userstyles.org/styles/90565/firefox-adjust-white-flash-when-opening-new-tab */

/* https://userstyles.org/styles/142191/remove-new-tab-flash */

@-moz-document url-prefix(about:preferences), url-prefix(about:blank), url-prefix(about:newtab) {

  html, body, #newtab-customize-overlay {

    background: #303030 !important;

    color: #b2b2b2 !important;

  } 

}



@-moz-document url(chrome://browser/content/browser.xul)

{



  browser[type="content-primary"]

  {

    background: #303030 !important;

    color: #b2b2b2 !important;

  }

}



@-moz-document url(chrome://browser/content/browser.xul)

{



  browser[type="content-primary"], tabbrowser tabpanels, #appcontent > #content

  {

    background: #1B1B1B url("chrome://global/skin/media/imagedoc-darknoise.png") repeat fixed !important;

    color: #b2b2b2 !important;

  }

}



@-moz-document url(about:blank),

               url(about:preferences),

               url(about:config),

               url(about:newtab)

{

  #newtab-window,

  html,

  body, 

  #newtab-customize-overlay 

  {

    background: #1B1B1B url("chrome://global/skin/media/imagedoc-darknoise.png") repeat fixed;

    color: #b2b2b2 !important;

  }

}



html>body {

  background: #303030 !important;

  color: #b2b2b2 !important;

}

Open about:config and change the value browser.display.background_color to the color of your choice. I'm using #595959 (neutral gray).

This works with blank tab or "Firefox Home".

Sadly, opening tab quickly or when the browser is on heavy load will still result of a white flash.

If you don't know how to use about:config please read https://support.mozilla.org/en-US/kb/about-config-editor-firefox

I like psychoslave's option but if u do not want to change the google background or those sites background what use the browser default background change the last three line like this:

#root{   background: #303030 !important;   color: #b2b2b2 !important; } 

And here is the full code, copyed from psychoslave's answer.

>     /* https://userstyles.org/styles/90565/firefox-adjust-white-flash-when-opening-new-tab

> */ /* https://userstyles.org/styles/142191/remove-new-tab-flash */ @-moz-document url-prefix(about:preferences), url-prefix(about:blank),

> url-prefix(about:newtab) {   html, body, #newtab-customize-overlay {

>     background: #303030 !important;

>     color: #b2b2b2 !important;   }  }

> 

> @-moz-document url(chrome://browser/content/browser.xul) {

> 

>   browser[type="content-primary"]   {

>     background: #303030 !important;

>     color: #b2b2b2 !important;   } }

> 

> @-moz-document url(chrome://browser/content/browser.xul) {

> 

>   browser[type="content-primary"], tabbrowser tabpanels, #appcontent >

> #content   {

>     background: #1B1B1B url("chrome://global/skin/media/imagedoc-darknoise.png") repeat fixed

> !important;

>     color: #b2b2b2 !important;   } }

> 

> @-moz-document url(about:blank),

>                url(about:preferences),

>                url(about:config),

>                url(about:newtab) {   #newtab-window,   html,   body,    #newtab-customize-overlay    {

>     background: #1B1B1B url("chrome://global/skin/media/imagedoc-darknoise.png") repeat fixed;

>     color: #b2b2b2 !important;   } }

> 

> #root {   background: #303030 !important;   color: #b2b2b2 !important; }