This site will have limited functionality while we undergo maintenance to improve your experience. If an article doesn't solve your issue and you want to ask a question, we have our support community waiting to help you at @FirefoxSupport on Twitter and/r/firefox on Reddit.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

Can Websites track my Theme?

  • 2 replies
  • 1 has this problem
  • 1 view
  • Last reply by Amelia

more options

Can websites i visit track my browsertheme for example system default or light or dark theme? I like the dark theme but i'm not using it because i fear it makes my browser much more unique, is that so? If so, is there a preference or another way to prefent websites from tracking my browser theme?

Can websites i visit track my browsertheme for example system default or light or dark theme? I like the dark theme but i'm not using it because i fear it makes my browser much more unique, is that so? If so, is there a preference or another way to prefent websites from tracking my browser theme?

Chosen solution

Yes, websites can see if you are using a dark or light theme via a css query, allowing javascript to find out and do something about it. For the nitty-gritty, look here https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme

the browser.theme.content-theme preference can be used to change what Firefox does when it comes to this, note it affects settings and internal pages. It is an integer value with the following meanings:

0: Dark mode on everything (except private browsing, that disallows dark mode like that altogether, but can be changed by another preference) 1: Light mode on everything 2: Follow system theme (detect what the system theme is and use that) -- Default 3: Follow Firefox theme (what color the tab text is in -- if the text is bright (white) it would contrast on black, and therefore would mean you have a dark theme)

Read this answer in context 👍 1

All Replies (2)

more options

Really? They can't? I think cor-el or jscher2000 told me they can, but then again how can i block that sort of spying? Any prefs?

more options

Chosen Solution

Yes, websites can see if you are using a dark or light theme via a css query, allowing javascript to find out and do something about it. For the nitty-gritty, look here https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme

the browser.theme.content-theme preference can be used to change what Firefox does when it comes to this, note it affects settings and internal pages. It is an integer value with the following meanings:

0: Dark mode on everything (except private browsing, that disallows dark mode like that altogether, but can be changed by another preference) 1: Light mode on everything 2: Follow system theme (detect what the system theme is and use that) -- Default 3: Follow Firefox theme (what color the tab text is in -- if the text is bright (white) it would contrast on black, and therefore would mean you have a dark theme)