urlbarViewScrollSelect.uc.js

// ==UserScript==
// @name           Scroll Urlbar Results with Mousewheel
// @version        1.0
// @author         aminomancer
// @homepage       https://github.com/aminomancer
// @description    Lets you navigate the results/suggestions in the urlbar with the mousewheel, (or trackpad scroll) and execute the active/selected result by right clicking anywhere in the urlbar panel. Makes one-hand operation easier.
// ==/UserScript==

(function () {
    let count = 0;
    let timer;

    /**
     * wheel callback
     * @param {object} e (wheel event)
     */
    function wheelSelect(e) {
        if (gURLBar.view.isOpen) {
            let dY = Math.abs(e.deltaY);
            let dX = Math.abs(e.deltaX);
            // check that the scroll input is mostly vertical. it's nearly impossible to send ONLY vertical or horizontal inputs on a trackpad, so we just use the dominant axis. if deltaX is bigger than deltaY then it's considered a horizontal scroll and it has no effect.
            if (dY > dX) {
                e.stopPropagation();
                e.preventDefault();
                if (dY % 1 === 0)
                    // actual mousewheel events should be integers, so we can just scroll one row per notch of the mousewheel.
                    gURLBar.view.selectBy(1, { reverse: e.deltaY < 0 });
                else {
                    // trackpad events will usually be decimals e.g. 0.333. since we can only scroll by one row at a time, there's no way to make the feedback proportional to the input. trackpads send lots of events with small delta values, while mousewheels send one event per "notch" with a delta value equal to the one set in your mouse settings. (at least on windows) my solution is to throttle the function for trackpad inputs. when scrolling finishes, set a 300ms timer that will nearly "empty" the throttle. that way the first event in a "new scroll" isn't throttled, the only events that get throttled are those in a fast, consecutive stream of wheel events.
                    window.clearTimeout(timer);
                    timer = window.setTimeout(() => {
                        count = 0.1;
                    }, 300);
                    // once the throttle reaches zero, scroll one row and "refill" the throttle.
                    if (count <= 0) {
                        gURLBar.view.selectBy(1, { reverse: e.deltaY < 0 });
                        count = 6;
                        return;
                    }
                    // reduce the throttle by an amount equal to the absolute value of deltaY. this is important because the rate at which scrolling on a trackpad sends wheel events doesn't seem to be correlated with the speed you move your fingers across the trackpad. so without this, you'd scroll through the rows at a constant speed, whether you're moving your fingers slowly or quickly. instead of making the speed proportional to the number of events per unit time, we make it proportional to the total deltaY. when you move your fingers slowly, you might send 5 events that only have deltaY of 0.33, but when you move your fingers over the same distance at a much faster speed, you'd still send 5 events but they'd have deltaY between of up to 20. by subtracting deltaY from the count, the number of events required before calling selectBy will be proportional to the deltaY of those events. a really fast scroll will be equivalent to count = 6 - 20 => -14, so the very next event will call selectBy. really slow scrolling will take much longer to count down to 0 from 6 since their deltaY is often less than 1.
                    count = count - dY;
                }
            }
        }
    }

    /**
     * right click callback
     * @param {object} e (mouseup event)
     */
    function rightClick(e) {
        if (gURLBar.view.isOpen && e.button === 2) {
            e.preventDefault();
            gURLBar.handleNavigation({ e }); // this method is how the urlbar handles pressing "enter" when a row is selected. if the row is a regular URL, it visits that URL. if the row is a search, it executes that search. if the row is a "switch to tab" item, then it switches to that tab, and so on.
        }
    }

    function init() {
        gURLBar.view._rows.addEventListener("wheel", wheelSelect, false);
        gURLBar.view._rows.addEventListener("mouseup", rightClick, false);
    }

    // wait until gURLBar is initialized to attach event listeners
    if (gBrowserInit.delayedStartupFinished) {
        setTimeout(init, 1000);
    } else {
        let delayedListener = (subject, topic) => {
            if (topic == "browser-delayed-startup-finished" && subject == window) {
                Services.obs.removeObserver(delayedListener, topic);
                setTimeout(init, 1000);
            }
        };
        Services.obs.addObserver(delayedListener, "browser-delayed-startup-finished");
    }
})();