Yes, zoom is proportional. Actually, when images are embedded in web pages, switching to text-only zoom should avoid zooming images. However, the stand-alone image viewer doesn't follow that rule.

You can reverse automatic scaling using a CSS transform. For example, if you have a default 125% scaling, then applying this rule to an image in the stand-alone viewer will force it to native size (setting aside the fact that large images shrink to fit):

    transform: scale(0.8);

If you are using Stylus or a similar extension that injects style rules, you could try this global style:

@-moz-document media-document(image) {
    body > img {
        transform: scale(0.8);
    }
}

If you have a different zoom level, or if you zoom that site, this will be the wrong number, so that is a complication. A more sophisticated rule might be able to handle it.

Note: that might require this settings change:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste moz-doc and pause while the list is filtered

(3) Double-click the layout.css.moz-document.content.enabled preference to switch the value from false to true

This rule counteracts zoom across a broader range. At the margins, it will be a little off, but you get the idea:

@-moz-document media-document(image) {
    /* 101% - 110% */
    @media (min-resolution: 97dpi) and (max-resolution: 106dpi) {
        body > img {
            transform: scale(0.90);
        }
    }
    /* 111% - 120% */
    @media (min-resolution: 107dpi) and (max-resolution: 116dpi) {
        body > img {
            transform: scale(0.88);
        }
    }
    /* 121% - 125% */
    @media (min-resolution: 116dpi) and (max-resolution: 120dpi) {
        body > img {
            transform: scale(0.8);
        }
    }
    /* 126% - 137% */
    @media (min-resolution: 121dpi) and (max-resolution: 131dpi) {
        body > img {
            transform: scale(0.732);
        }
    }
    /* 138% - 150% */
    @media (min-resolution: 132dpi) and (max-resolution: 144dpi) {
        body > img {
            transform: scale(0.67);
        }
    }
    /* 151% - 167% */
    @media (min-resolution: 145dpi) and (max-resolution: 160dpi) {
        body > img {
            transform: scale(0.6);
        }
    }
}

This is a complaint that this should be fixed and a person shouldn't have to modify a program to behave in a logical way. And those solutions don't seem like some of them could produce pixel-perfect output...

Here in support, we work with the Firefox we have today. We can suggest features, settings, add-ons, and other workarounds. If you want to suggest feature changes to future versions of Firefox, you can submit comments through one or more of the following links:

• Feedback: https://qsurvey.mozilla.com/s3/FirefoxInput/
• Discourse: https://discourse.mozilla.org/c/firefox-development
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