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How to set PDF viewer in firefox to dark mode again (after it stopped working)

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  • آخر ردّ كتبه cor-el

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I view a lot of pdf documents via firefox, the light gray background makes my eyes and head hurt after prolonged usage. In the past I found a solution on this forum that advised to set pdfjs.viewerCssTheme to "2" in about:config. This set the background of pdf viewer to black/dark gray. This has worked for years until recently when the pdf viewer switched to light mode again (pic 1). I checked the about:config settings for pdfjs.viewerCssTheme but there appears to be no change. I tried restarting the browser, setting the theme to 0 and to 2 again, updating browser. Sadly the theme is still light gray. Is there a way to change it again? The desired outcome is in pic 2. I do NOT want to change the color of the pdf pages themselves.

I view a lot of pdf documents via firefox, the light gray background makes my eyes and head hurt after prolonged usage. In the past I found a solution on this forum that advised to set pdfjs.viewerCssTheme to "2" in about:config. This set the background of pdf viewer to black/dark gray. This has worked for years until recently when the pdf viewer switched to light mode again (pic 1). I checked the about:config settings for pdfjs.viewerCssTheme but there appears to be no change. I tried restarting the browser, setting the theme to 0 and to 2 again, updating browser. Sadly the theme is still light gray. Is there a way to change it again? The desired outcome is in pic 2. I do NOT want to change the color of the pdf pages themselves.
Attached screenshots

Modified by K

الحل المُختار

The pdfjs.viewerCssTheme setting was removed in Firefox 121 for being partially broken (Bug 1863201).

You can change the PDF viewer background color with userContent.css:

@-moz-document unobservable-document() {
  body:has(.pdfViewer) {
    background-color: rgb(42 42 46) !important;
  }
}
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All Replies (7)

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K said

I view a lot of pdf documents via firefox, the light gray background makes my eyes and head hurt after prolonged usage. In the past I found a solution on this forum that advised to set pdfjs.viewerCssTheme to "2" in about:config. This set the background of pdf viewer to black/dark gray. This has worked for years until recently when the pdf viewer switched to light mode again (pic 1). I checked the about:config settings for pdfjs.viewerCssTheme but there appears to be no change. I tried restarting the browser, setting the theme to 0 and to 2 again, updating browser. Sadly the theme is still light gray. Is there a way to change it again? The desired outcome is in pic 2. I do NOT want to change the color of the pdf pages themselves.
for some reason uploading the pictures changed their order. I hope the context still makes my question clear
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الحل المُختار

The pdfjs.viewerCssTheme setting was removed in Firefox 121 for being partially broken (Bug 1863201).

You can change the PDF viewer background color with userContent.css:

@-moz-document unobservable-document() {
  body:has(.pdfViewer) {
    background-color: rgb(42 42 46) !important;
  }
}
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@zeroknight Thank you for your help, this worked really well! This is only a small thing, but is there also a way to change the color of the toolbar container at the top of the pdf viewer? I suppose I would have to change both the color of the container and the color of the text.. if this would be too problematic, then no problem. I'm glad I could change the color of the background at all

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This is based on an older approach, which is to take all of the dark theme rules -- the ones Firefox would use if you went to the Web Appearance section of the Settings page and selected Dark -- and stuff those into your userContent.css file.

/*** Firefox 121 PDF Viewer Dark Theme for userContent.css ***/
/* 

    These rules are from 
    resource://pdf.js/web/viewer.css or
    https://searchfox.org/mozilla-release/source/toolkit/components/pdfjs/content/web/viewer.css
    Lines within:
    @media (prefers-color-scheme: dark) {}

 */
@-moz-document unobservable-document() {
  body:has(.pdfViewer) {
    --main-color:rgb(249 249 250);
    --body-bg-color:rgb(42 42 46);
    --progressBar-color:rgb(0 96 223);
    --progressBar-bg-color:rgb(40 40 43);
    --progressBar-blend-color:rgb(20 68 133);
    --scrollbar-color:rgb(121 121 123);
    --scrollbar-bg-color:rgb(35 35 39);
    --toolbar-icon-bg-color:rgb(255 255 255);
    --toolbar-icon-hover-bg-color:rgb(255 255 255);
    --sidebar-narrow-bg-color:rgb(42 42 46 / 0.9);
    --sidebar-toolbar-bg-color:rgb(50 50 52);
    --toolbar-bg-color:rgb(56 56 61);
    --toolbar-border-color:rgb(12 12 13);
    --button-hover-color:rgb(102 102 103);
    --toggled-btn-color:rgb(255 255 255);
    --toggled-btn-bg-color:rgb(0 0 0 / 0.3);
    --toggled-hover-active-btn-color:rgb(0 0 0 / 0.4);
    --dropdown-btn-bg-color:rgb(74 74 79);
    --separator-color:rgb(0 0 0 / 0.3);
    --field-color:rgb(250 250 250);
    --field-bg-color:rgb(64 64 68);
    --field-border-color:rgb(115 115 115);
    --treeitem-color:rgb(255 255 255 / 0.8);
    --treeitem-bg-color:rgb(255 255 255 / 0.15);
    --treeitem-hover-color:rgb(255 255 255 / 0.9);
    --treeitem-selected-color:rgb(255 255 255 / 0.9);
    --treeitem-selected-bg-color:rgb(255 255 255 / 0.25);
    --thumbnail-hover-color:rgb(255 255 255 / 0.1);
    --thumbnail-selected-color:rgb(255 255 255 / 0.2);
    --doorhanger-bg-color:rgb(74 74 79);
    --doorhanger-border-color:rgb(39 39 43);
    --doorhanger-hover-color:rgb(249 249 250);
    --doorhanger-hover-bg-color:rgb(93 94 98);
    --doorhanger-separator-color:rgb(92 92 97);
    --dialog-button-bg-color:rgb(92 92 97);
    --dialog-button-hover-bg-color:rgb(115 115 115);
    --loading-icon:url(images/loading-dark.svg);
    --editor-toolbar-bg-color:#2b2a33;
    --editor-toolbar-fg-color:#fbfbfe;
    --editor-toolbar-border-color:#2b2a33;
    --editor-toolbar-hover-bg-color:#52525e;
    --editor-toolbar-active-bg-color:#5b5b66;
    --editor-toolbar-focus-outline-color:#0df;
    --alt-text-tooltip-bg:#1c1b22;
    --alt-text-tooltip-fg:#fbfbfe;
    --alt-text-tooltip-shadow:0px 2px 6px 0px #15141a;
    --dialog-bg-color:#1c1b22;
    --dialog-border-color:#1c1b22;
    --dialog-shadow:0 2px 14px 0 #15141a;
    --text-primary-color:#fbfbfe;
    --text-secondary-color:#cfcfd8;
    --focus-ring-color:#0df;
    --hover-filter:brightness(1.4);
    --textarea-bg-color:#42414d;
    --radio-bg-color:#2b2a33;
    --radio-checked-bg-color:#15141a;
    --radio-checked-border-color:#0df;
    --button-cancel-bg-color:#2b2a33;
    --button-save-bg-color:#0df;
    --button-save-fg-color:#15141a;
  }
}
/*** END PDF Viewer DARK THEME ***/
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jscher2000 - Support Volunteer said

take all of the dark theme rules and stuff those into your userContent.css file.

Only do this if you are prepared to maintain it long-term. It will break every time colors are changed between versions, anything from minor cosmetic issues to major usability issues due to invisible controls.

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zeroknight said

The pdfjs.viewerCssTheme setting was removed in Firefox 121 for being partially broken (Bug 1863201). You can change the PDF viewer background color with userContent.css: @-moz-document unobservable-document() { body:has(.pdfViewer) { background-color: rgb(42 42 46) !important; } }

This CSS snippet is better:

@media (prefers-color-scheme: dark){

  .pdfViewer{filter: invert(1) hue-rotate(180deg);}

}

Modified by luo.chuan

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^: note that your CSS code also affects images, what may not be what you want in case of a PDF file with images.

You can also look at these two pdfjs.pageColors prefs in about:config.

  • pdfjs.pageColorsBackground Canvas (#FFFFFF) => #000
  • pdfjs.pageColorsForeground CanvasText (#000000) => #FFF