diff --git a/web/app.js b/web/app.js
index 684f29bfb..4c0bc95bf 100644
--- a/web/app.js
+++ b/web/app.js
@@ -217,7 +217,9 @@ const PDFViewerApplication = {
   _contentLength: null,
   _saveInProgress: false,
   _wheelUnusedTicks: 0,
+  _wheelUnusedFactor: 1,
   _touchUnusedTicks: 0,
+  _touchUnusedFactor: 1,
   _PDFBug: null,
   _hasAnnotationEditors: false,
   _title: document.title,
@@ -2058,6 +2060,23 @@ const PDFViewerApplication = {
     return wholeTicks;
   },
 
+  _accumulateFactor(previousScale, factor, prop) {
+    if (factor === 1) {
+      return 1;
+    }
+    // If the direction changed, reset the accumulated factor.
+    if ((this[prop] > 1 && factor < 1) || (this[prop] < 1 && factor > 1)) {
+      this[prop] = 1;
+    }
+
+    const newFactor =
+      Math.floor(previousScale * factor * this[prop] * 100) /
+      (100 * previousScale);
+    this[prop] = factor / newFactor;
+
+    return newFactor;
+  },
+
   /**
    * Should be called *after* all pages have loaded, or if an error occurred,
    * to unblock the "load" event; see https://bugzilla.mozilla.org/show_bug.cgi?id=1618553
@@ -2628,8 +2647,11 @@ function setZoomDisabledTimeout() {
 }
 
 function webViewerWheel(evt) {
-  const { pdfViewer, supportedMouseWheelZoomModifierKeys } =
-    PDFViewerApplication;
+  const {
+    pdfViewer,
+    supportedMouseWheelZoomModifierKeys,
+    supportsPinchToZoom,
+  } = PDFViewerApplication;
 
   if (pdfViewer.isInPresentationMode) {
     return;
@@ -2653,45 +2675,61 @@ function webViewerWheel(evt) {
       return;
     }
 
-    // It is important that we query deltaMode before delta{X,Y}, so that
-    // Firefox doesn't switch to DOM_DELTA_PIXEL mode for compat with other
-    // browsers, see https://bugzilla.mozilla.org/show_bug.cgi?id=1392460.
-    const deltaMode = evt.deltaMode;
-    const delta = normalizeWheelEventDirection(evt);
     const previousScale = pdfViewer.currentScale;
+    if (isPinchToZoom && supportsPinchToZoom) {
+      // The following formula is a bit strange but it comes from:
+      // https://searchfox.org/mozilla-central/rev/d62c4c4d5547064487006a1506287da394b64724/widget/InputData.cpp#618-626
+      let scaleFactor = Math.exp(-evt.deltaY / 100);
+      scaleFactor = PDFViewerApplication._accumulateFactor(
+        previousScale,
+        scaleFactor,
+        "_wheelUnusedFactor"
+      );
+      if (scaleFactor < 1) {
+        PDFViewerApplication.zoomOut(null, scaleFactor);
+      } else if (scaleFactor > 1) {
+        PDFViewerApplication.zoomIn(null, scaleFactor);
+      }
+    } else {
+      // It is important that we query deltaMode before delta{X,Y}, so that
+      // Firefox doesn't switch to DOM_DELTA_PIXEL mode for compat with other
+      // browsers, see https://bugzilla.mozilla.org/show_bug.cgi?id=1392460.
+      const deltaMode = evt.deltaMode;
+      const delta = normalizeWheelEventDirection(evt);
 
-    let ticks = 0;
-    if (
-      deltaMode === WheelEvent.DOM_DELTA_LINE ||
-      deltaMode === WheelEvent.DOM_DELTA_PAGE
-    ) {
-      // For line-based devices, use one tick per event, because different
-      // OSs have different defaults for the number lines. But we generally
-      // want one "clicky" roll of the wheel (which produces one event) to
-      // adjust the zoom by one step.
-      if (Math.abs(delta) >= 1) {
-        ticks = Math.sign(delta);
+      let ticks = 0;
+      if (
+        deltaMode === WheelEvent.DOM_DELTA_LINE ||
+        deltaMode === WheelEvent.DOM_DELTA_PAGE
+      ) {
+        // For line-based devices, use one tick per event, because different
+        // OSs have different defaults for the number lines. But we generally
+        // want one "clicky" roll of the wheel (which produces one event) to
+        // adjust the zoom by one step.
+        if (Math.abs(delta) >= 1) {
+          ticks = Math.sign(delta);
+        } else {
+          // If we're getting fractional lines (I can't think of a scenario
+          // this might actually happen), be safe and use the accumulator.
+          ticks = PDFViewerApplication._accumulateTicks(
+            delta,
+            "_wheelUnusedTicks"
+          );
+        }
       } else {
-        // If we're getting fractional lines (I can't think of a scenario
-        // this might actually happen), be safe and use the accumulator.
+        // pixel-based devices
+        const PIXELS_PER_LINE_SCALE = 30;
         ticks = PDFViewerApplication._accumulateTicks(
-          delta,
+          delta / PIXELS_PER_LINE_SCALE,
           "_wheelUnusedTicks"
         );
       }
-    } else {
-      // pixel-based devices
-      const PIXELS_PER_LINE_SCALE = 30;
-      ticks = PDFViewerApplication._accumulateTicks(
-        delta / PIXELS_PER_LINE_SCALE,
-        "_wheelUnusedTicks"
-      );
-    }
 
-    if (ticks < 0) {
-      PDFViewerApplication.zoomOut(-ticks);
-    } else if (ticks > 0) {
-      PDFViewerApplication.zoomIn(ticks);
+      if (ticks < 0) {
+        PDFViewerApplication.zoomOut(-ticks);
+      } else if (ticks > 0) {
+        PDFViewerApplication.zoomIn(ticks);
+      }
     }
 
     const currentScale = pdfViewer.currentScale;
@@ -2725,12 +2763,15 @@ function webViewerTouchStart(evt) {
     return;
   }
 
-  const [touch0, touch1] = evt.touches;
+  let [touch0, touch1] = evt.touches;
+  if (touch0.identifier > touch1.identifier) {
+    [touch0, touch1] = [touch1, touch0];
+  }
   PDFViewerApplication._touchInfo = {
-    centerX: (touch0.pageX + touch1.pageX) / 2,
-    centerY: (touch0.pageY + touch1.pageY) / 2,
-    distance:
-      Math.hypot(touch0.pageX - touch1.pageX, touch0.pageY - touch1.pageY) || 1,
+    touch0X: touch0.pageX,
+    touch0Y: touch0.pageY,
+    touch1X: touch1.pageX,
+    touch1Y: touch1.pageY,
   };
 }
 
@@ -2740,42 +2781,88 @@ function webViewerTouchMove(evt) {
   }
 
   const { pdfViewer, _touchInfo, supportsPinchToZoom } = PDFViewerApplication;
-  const [touch0, touch1] = evt.touches;
+  let [touch0, touch1] = evt.touches;
+  if (touch0.identifier > touch1.identifier) {
+    [touch0, touch1] = [touch1, touch0];
+  }
   const { pageX: page0X, pageY: page0Y } = touch0;
   const { pageX: page1X, pageY: page1Y } = touch1;
-  const distance = Math.hypot(page0X - page1X, page0Y - page1Y) || 1;
-  const { distance: previousDistance } = _touchInfo;
-  const scaleFactor = distance / previousDistance;
+  const {
+    touch0X: pTouch0X,
+    touch0Y: pTouch0Y,
+    touch1X: pTouch1X,
+    touch1Y: pTouch1Y,
+  } = _touchInfo;
 
-  if (supportsPinchToZoom && Math.abs(scaleFactor - 1) <= 1e-2) {
-    // Scale increase/decrease isn't significant enough.
+  if (
+    Math.abs(pTouch0X - page0X) <= 1 &&
+    Math.abs(pTouch0Y - page0Y) <= 1 &&
+    Math.abs(pTouch1X - page1X) <= 1 &&
+    Math.abs(pTouch1Y - page1Y) <= 1
+  ) {
+    // Touches are really too close and it's hard do some basic
+    // geometry in order to guess something.
     return;
   }
 
-  const { centerX, centerY } = _touchInfo;
-  const diff0X = page0X - centerX;
-  const diff1X = page1X - centerX;
-  const diff0Y = page0Y - centerY;
-  const diff1Y = page1Y - centerY;
-  const dotProduct = diff0X * diff1X + diff0Y * diff1Y;
-  if (dotProduct >= 0) {
-    // The two touches go in almost the same direction.
-    return;
+  _touchInfo.touch0X = page0X;
+  _touchInfo.touch0Y = page0Y;
+  _touchInfo.touch1X = page1X;
+  _touchInfo.touch1Y = page1Y;
+
+  if (pTouch0X === page0X && pTouch0Y === page0Y) {
+    // First touch is fixed, if the vectors are collinear then we've a pinch.
+    const v1X = pTouch1X - page0X;
+    const v1Y = pTouch1Y - page0Y;
+    const v2X = page1X - page0X;
+    const v2Y = page1Y - page0Y;
+    const det = v1X * v2Y - v1Y * v2X;
+    // 0.02 is approximatively sin(0.15deg).
+    if (Math.abs(det) > 0.02 * Math.hypot(v1X, v1Y) * Math.hypot(v2X, v2Y)) {
+      return;
+    }
+  } else if (pTouch1X === page1X && pTouch1Y === page1Y) {
+    // Second touch is fixed, if the vectors are collinear then we've a pinch.
+    const v1X = pTouch0X - page1X;
+    const v1Y = pTouch0Y - page1Y;
+    const v2X = page0X - page1X;
+    const v2Y = page0Y - page1Y;
+    const det = v1X * v2Y - v1Y * v2X;
+    if (Math.abs(det) > 0.02 * Math.hypot(v1X, v1Y) * Math.hypot(v2X, v2Y)) {
+      return;
+    }
+  } else {
+    const diff0X = page0X - pTouch0X;
+    const diff1X = page1X - pTouch1X;
+    const diff0Y = page0Y - pTouch0Y;
+    const diff1Y = page1Y - pTouch1Y;
+    const dotProduct = diff0X * diff1X + diff0Y * diff1Y;
+    if (dotProduct >= 0) {
+      // The two touches go in almost the same direction.
+      return;
+    }
   }
 
   evt.preventDefault();
 
+  const distance = Math.hypot(page0X - page1X, page0Y - page1Y) || 1;
+  const pDistance = Math.hypot(pTouch0X - pTouch1X, pTouch0Y - pTouch1Y) || 1;
   const previousScale = pdfViewer.currentScale;
   if (supportsPinchToZoom) {
-    if (scaleFactor < 1) {
-      PDFViewerApplication.zoomOut(null, scaleFactor);
-    } else {
-      PDFViewerApplication.zoomIn(null, scaleFactor);
+    const newScaleFactor = PDFViewerApplication._accumulateFactor(
+      previousScale,
+      distance / pDistance,
+      "_touchUnusedFactor"
+    );
+    if (newScaleFactor < 1) {
+      PDFViewerApplication.zoomOut(null, newScaleFactor);
+    } else if (newScaleFactor > 1) {
+      PDFViewerApplication.zoomIn(null, newScaleFactor);
     }
   } else {
     const PIXELS_PER_LINE_SCALE = 30;
     const ticks = PDFViewerApplication._accumulateTicks(
-      (distance - previousDistance) / PIXELS_PER_LINE_SCALE,
+      (distance - pDistance) / PIXELS_PER_LINE_SCALE,
       "_touchUnusedTicks"
     );
     if (ticks < 0) {
@@ -2788,9 +2875,8 @@ function webViewerTouchMove(evt) {
   const currentScale = pdfViewer.currentScale;
   if (previousScale !== currentScale) {
     const scaleCorrectionFactor = currentScale / previousScale - 1;
-    const newCenterX = (_touchInfo.centerX = (page0X + page1X) / 2);
-    const newCenterY = (_touchInfo.centerY = (page0Y + page1Y) / 2);
-    _touchInfo.distance = distance;
+    const newCenterX = (page0X + page1X) / 2;
+    const newCenterY = (page0Y + page1Y) / 2;
 
     const [top, left] = pdfViewer.containerTopLeft;
     const dx = newCenterX - left;
@@ -2807,8 +2893,8 @@ function webViewerTouchEnd(evt) {
 
   evt.preventDefault();
   PDFViewerApplication._touchInfo = null;
-  PDFViewerApplication.pdfViewer.refresh();
   PDFViewerApplication._touchUnusedTicks = 0;
+  PDFViewerApplication._touchUnusedFactor = 1;
 }
 
 function webViewerClick(evt) {