A person sitting in a dark room, their face illuminated by a bright laptop screen.

If you love dark mode for eye-friendly late-night browsing and you also love Mozilla Firefox, you’ve likely come across a problem: opening new tabs and loading new pages blinds you. Here’s how to make new tabs dark-mode friendly.

Dark Mode Is Great, but The White “Flash” Isn’t

There’s a problem with Firefox’s dark mode that persists, despite various bug fixes over the last few years. If you’re not a devoted dark mode user, you might not be familiar with this problem. If you are—and, I certainly am—you’re probably thrilled to find out there’s a simple solution that works whether the bug gets fully squashed or not.

The problem? Even if you have Firefox in dark mode, whenever you open a new blank tab, it is blindingly white.

Worse, even when you’re loading a web page that supports dark mode, there is a brief “flash” where the default white background blasts bright white light out at you before the page loads.

That might not seem like the end of the world, but when you’ve carefully tuned your workspace specifically to avoid your very bright monitor blasting you in the face with bright white light, it’s a bit jarring.

So forget being startled late at night while you’re peacefully working in dark mode. Let’s deploy a simple fix to ensure those high-lumen sneak attacks are a thing of the past.

Forget Browser Extensions, Modify Your Chrome Instead

When it comes to your web browser, if you can solve something in the simplest possible way using the least amount of risk, then it is always for the best. Browser extensions are a security and privacy nightmare.

While you don’t have to avoid them entirely, sticking only to add-ons and extensions that are properly reviewed and verified is wise. It’s always a safe bet to avoid random extensions from unknown authors.

With that in mind, we were really happy to find an unbelievably simple way to solve our problem without having to search out (and review the code of) an extension custom coded for the task.

The solution? Taking advantage of a handy little browser modification tool built right into Firefox, the userChrome.css and userContent.css files.

If you pick apart that first file name, you get a clue as to what we’re about to do, it’s a user-supplied style-sheet for the browser’s chrome. (The Chrome web browser is actually named after the browser chrome, and it’s a bit of a joke, at that.) We’ll also, in the name of thoroughness, be modifying the userContent.css , too.

Enable Legacy Style Support

Before anything else, we need to toggle on a configuration setting so that our little tweak will actually take effect. If you don’t do this step, you’ll be tearing your hair out in frustration when none of the changes we make do anything.

Launch Firefox and type about:config in the address bar. Dismiss the warning if it appears. Use the search box to search for toolkit.legacyUserProfileCustomizations.stylesheets . The default value is false, double click the entry to set it to true.

Locate Your Profile Directory

First, we need to locate where the configuration files for your particular Firefox installation. Launch Firefox and type  about:profiles in the address bar. This will list all your Firefox browser profiles and provide a handy direct link to the root directory for your profile.

Select the profile you wish to perform this dark mode tweak on and click the “Open Folder” button next to the list entry for “Root Directory.”

For Windows users, this directory will look something like  C:\Users\[YourUserName]\AppData\Roaming\Mozilla\Firefox\Profiles\[ProfileName] where YourUserName is your Windows username, and ProfileName is an alphanumeric string generated by Firefox like fxxd088p.default-release .

Create Chrome Directory and Style Files

If you search for style sheet solutions to this particular problem, there are several variations floating around—some needlessly complex—but we’ve been using the very simple code snippets shared by github user gmolveau for years now with great success and recommend you do the same.

Within the profile directory, create a new sub-directory called chrome. We will be creating two style sheet files within that directory.

Create a new blank text document in that directory and paste the following code into it:

tabbrowser tabpanels { background-color: rgb(19,19,20) !important; }
browser { background-color: #131314 !important; }

Save the file with the name userChrome.css. This bit of code will fix the bright white flicker that occurs between page loads.

Create another blank text document and paste this code:

@-moz-document url-prefix(about:blank) {
    html > body:empty {
        background-color: rgb(19,19,20) !important;
@-moz-document url(about:blank) {
    html > body:empty {
        background-color: rgb(19,19,20) !important;

Save the file with the name userContent.css. This bit of code will ensure that blank tabs are a very dark muted gray and not bright white.

You can replace the muted gray with any color you wish using appropriate RGB and hex codes. If you wanted jet black, for instance, you could replace every instance of 19,19,20 above with 0,0,0 and every instance of #131314 with #0A0A0A.

Or, if you wanted to cast a vote for total anarchy, we suppose, you could go with neon green: 117,225,51 #75FF33 . Whatever your color desire, you can use a simple RGB picker to select the right codes.

Once you’ve created the files, simply restart Firefox for the changes to take effect (if they don’t take effect, make sure you enabled legacy support as outlined in the first step).

Now you can test it. You can check what color the blank tab is in your Firefox install by typing about:blank in the address bar.

Testing the page loading “flash” is a bit trickier. The easiest way to test it is to visit a web page and open a few links from that page in new tabs.

Sometimes it’s hard to catch, especially on a fast connection to an optimized web page, but if you load a few, you should be able to catch the color change—in the screenshot above, you can see how the flash of color between page loads is no longer white but the muted gray we selected.

If, after all this, you’ve really got dark mode on the mind, now’s a perfect time to enable dark mode everywhere.

Profile Photo for Jason Fitzpatrick Jason Fitzpatrick
Jason Fitzpatrick is the Senior Smart Home Editor at How-To Geek. He has over a decade of experience in publishing and has authored thousands of articles at How-To Geek, Review Geek, LifeSavvy, and Lifehacker. Jason served as Lifehacker's Weekend Editor before he joined How-To Geek.
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