43

Is there a built-in way in Firefox to blacken or to colour the about:blank page?

Will I maybe save some energy by doing so?

52

Under about:config, change browser.display.background_color from #ffffff to whatever hex value you want.

Changing screen space to a dark color (preferably black) will ONLY make a power difference when using AMOLED screens, most commonly found on phones. So if you're using a regular LCD, TFT or, IPS display, you won't see any battery life improvements, but your browser will be swagged out

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  • Did not work for me on Firefox 69 on Ubuntu Linux 18.04. Furthermore, as explained on kb.mozillazine.org/About:config_entries#Browser this setting can actually be changed in the regular user preference panel. – Stéphane Gourichon Oct 8 '19 at 12:09
  • 7
    To be more precise, this settings applies either "only to pages that don't specify a color" or "on all pages only when using a high contrast theme" or "on all pages". We don't want it "on all pages", only on new blank tab. – Stéphane Gourichon Oct 9 '19 at 6:51
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    This breaks the background color on pages like wolframalpha.com and many others, making them potentially unreadable. The accepted answer, or the one at gist.github.com/gmolveau/a802ded1320a7591a289fb7abd0d6c45, works correctly. – erb Jan 9 at 15:15
  • Although this will break the background for any web page without default background, when using plugins like DarkReader to make all pages dark, it can work out well. – Sushruth Jan 30 at 8:10
  • Do you know a way to do this on Google Chrome? – Jire Jun 10 at 0:04
35

Yes you can change the color. As explained here you should

  1. Windows: go to %appdata%/mozilla/firefox/profiles and open the folder in there.

    On Linux the equivalent is ~/.mozilla/firefox/RANDOM_TEXT.default/

    On OSX it is /Library/Application Support/Firefox/Profiles/RANDOM_TEXT.default

  2. look for the chrome folder. In that folder, find userContent-example.css and rename it to userContent.css.

    The folder and file may not be there yet with newer Firefox versions. If so, simply create them manually.

  3. Add this line to the file

    @-moz-document url-prefix(about:blank) {*{background-color:#000000;}}
    

As to whether it will save energy, probably not:

On LCD displays, color may confer no benefit at all. In response to my inquiry, Steve Ryan, program manager for Energy Star’s power-management program, asked consulting firm Cadmus Group to run a quick test by loading Blackle, Google and the Web site of the New York Times (which is, like Google, mostly white on-screen) on two monitors — one CRT, one LCD — and connecting a power meter to both. “We found that the color on screen mattered very little to the energy color consumption of the LCD monitor,” said David Korn, principal at Cadmus, which specializes in energy and environment, and does work for the government. The changes were so slight as to be within the margin of error for the power meter. Tweaking brightness and contrast and settings had a bigger effect. The bulkier CRT screen did see savings with Blackle of between 5% and 20%. Mr. Korn emphasized that this was a quick test, not a rigorous study.

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  • Woohoo :D It worked! Thank you very much! On my Mac it was /Library/Application Support/Firefox/Profiles/123xyz.default. I had to manually create the chrome folder and placed your CSS file in there, restart and it worked! Thanks! – leymannx Jun 3 '13 at 17:35
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    The disadvantage of setting the background-colour is, that especially on websites with text entry fields the background of the text will also appear in that background-colour... In other words: websites where no CSS background colour is set, the background colour is the Firefox background-colour. Makes typing/reading quite uncomfortable. So I set it back to default by deleting the userContent.css – leymannx Jul 3 '13 at 9:20
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    Easier way to open profile folder: open "about:support" page in Firefox and click the "Profile Folder" button. – ciastek Jan 3 '17 at 0:00
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    It works for Firefox 57 also, just chreate the chrome/userConent.css file if it doesn't exist. – tigerjack89 Nov 30 '17 at 20:45
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    As far as I know, this trick no longer works on Firefox 67. – Mercury Platinum Jun 5 '19 at 20:43
15

If you have Stylus extension installed, just create a new style with this exact code:

@-moz-document url-prefix(about:blank) {*{background-color:#000000;}}

credit goes to terdon's answer


Update: Apparently, what Stylus says in its message about how this no longer works on special pages like about:blank, it actually still totally does! To add a script, you have to use the workaround proposed by mic in comments:

  • Open the Manage page of Stylus with the list of all scripts you have;
  • Press "Write new style" button;
  • Under the large "Mozilla format" header press the "Import" button, and a popup with a textbox will open, paste the entire script from this post into it, and press "overwrite style"
  • Don't forget to add a descriptive name for the script in the top left textbox;
  • Press "Save".
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  • 3
    +1 This should be up voted more. In v38 of Firefox it should be about:newtab – L84 May 4 '15 at 17:32
  • That is if you wish for your new tab to be about:newtab. I set it to about:blank myself. – user1306322 May 4 '15 at 18:41
  • True but my about:blank page and new tab are one and the same for me, at least with the way I use FF. => – L84 May 4 '15 at 20:37
  • I added both about:newtab and about:blank to have all of my tab start with black background: @-moz-document url-prefix(about:newtab) {*{background-color:#000000;}} @-moz-document url-prefix(about:blank) {*{background-color:#000000;}} – Kamran Bigdely May 13 '16 at 3:16
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    You can still use Stylus and write a style for about:blank and the style will work, despite the message from Stylus. You just have to go to Manage > Write > Import > [Paste in the code] Overwrite style, and name your style and save. (Firefox 68) – mic Jul 26 '19 at 11:38
6

I know this is an old question, but in Firefox 64, the chrome folder doesn't exist anymore in the /Library/Application Support/Firefox/Profiles/RANDOM_TEXT.default location.

I did find a setting though under the about:config key browser.display.background_color, which you can set to any hex color code. This setting will probably save my eyes a couple dozen times a day.

HTH

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  • Works great - thanks! Takes effect at the moment the about:config tab is closed. – jcoppens Jun 11 '19 at 5:30
  • You can just create the chrome folder and the userChrome.css file. – Casey Jones Jun 29 '19 at 3:11
  • chrome.css is apparently going to be disabled by default in the near future, but you can re-enable it via about:config settings bugzilla.mozilla.org/show_bug.cgi?id=1541233 – user1306322 Aug 24 '19 at 18:48
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    This isn't working for me on FF 68.0.2 (64-bit, Ubuntu 16.04). – TenLeftFingers Aug 24 '19 at 21:09
  • background_color is the settings mentioned in @fredthefaillord and doesn't work on recent firefox. – Stéphane Gourichon Oct 9 '19 at 6:53
2

Set browser.display.use_system_colors to true in about:config.

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  • Did not work for me on Firefox 69 on Ubuntu Linux 18.04. – Stéphane Gourichon Oct 9 '19 at 6:54
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    Your system theme should be dark of course. – sergio Oct 10 '19 at 10:24
  • Before writing here, I tried dark system theme with default firefox theme which follows it, then with firefox dark theme, did not work either. Thanks for mentioning this anyway. – Stéphane Gourichon Oct 10 '19 at 14:00
  • I could kiss you – cutie Oct 22 at 15:58
1

In Linux, add the following file (or append to it, if it exists):

~/.config/gtk-3.0/settings.ini

[Settings]
gtk-application-prefer-dark-theme = true

(you might also find and toggle this option through your Linux distro settings manager)

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