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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?

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up vote 16 down vote accepted

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
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

If you have Stylish 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

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+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;}} – kami May 13 at 3:16

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