diff --git a/client/app/scripts/components/time-travel-timeline.js b/client/app/scripts/components/time-travel-timeline.js
index 68b77f434a..b7dbbacfc5 100644
--- a/client/app/scripts/components/time-travel-timeline.js
+++ b/client/app/scripts/components/time-travel-timeline.js
@@ -8,7 +8,7 @@ import { scaleUtc } from 'd3-scale';
 import { event as d3Event, select } from 'd3-selection';
 import { Motion, spring } from 'react-motion';
 
-import { defaultWheelDelta } from '../utils/zoom-utils';
+import { zoomFactor } from '../utils/zoom-utils';
 import { linearGradientValue } from '../utils/math-utils';
 import { trackMixpanelEvent } from '../utils/tracking-utils';
 import {
@@ -66,7 +66,6 @@ const INIT_DURATION_PER_PX = moment.duration(1, 'minute');
 const MAX_DURATION_PER_PX = moment.duration(3, 'days');
 const MIN_TICK_SPACING_PX = 70;
 const MAX_TICK_SPACING_PX = 415;
-const ZOOM_SENSITIVITY = 2;
 const FADE_OUT_FACTOR = 1.4;
 const TICKS_ROW_SPACING = 16;
 const MAX_TICK_ROWS = 3;
@@ -169,8 +168,7 @@ class TimeTravelTimeline extends React.Component {
   }
 
   handleZoom(ev) {
-    const scale = Math.pow(ZOOM_SENSITIVITY, defaultWheelDelta(ev));
-    let durationPerPixel = scaleDuration(this.state.durationPerPixel, scale);
+    let durationPerPixel = scaleDuration(this.state.durationPerPixel, zoomFactor(ev));
     if (durationPerPixel > MAX_DURATION_PER_PX) durationPerPixel = MAX_DURATION_PER_PX;
     if (durationPerPixel < MIN_DURATION_PER_PX) durationPerPixel = MIN_DURATION_PER_PX;
 
diff --git a/client/app/scripts/utils/zoom-utils.js b/client/app/scripts/utils/zoom-utils.js
index a4a5afcb7f..043d59a65e 100644
--- a/client/app/scripts/utils/zoom-utils.js
+++ b/client/app/scripts/utils/zoom-utils.js
@@ -1,5 +1,15 @@
 
+const ZOOM_SENSITIVITY = 0.0025;
+const DOM_DELTA_LINE = 1;
+
 // See https://github.com/d3/d3-zoom/blob/807f02c7a5fe496fbd08cc3417b62905a8ce95fa/src/zoom.js
-export function defaultWheelDelta(ev) {
-  return ev.deltaY * (ev.deltaMode ? 120 : 1) * 0.002;
+function wheelDelta(ev) {
+  // Only Firefox seems to use the line unit (which we assume to
+  // be 25px), otherwise the delta is already measured in pixels.
+  const unitInPixels = (ev.deltaMode === DOM_DELTA_LINE ? 25 : 1);
+  return ev.deltaY * unitInPixels * ZOOM_SENSITIVITY;
+}
+
+export function zoomFactor(ev) {
+  return Math.exp(wheelDelta(ev));
 }