diff --git a/ui-charts/src/manchette/hooks/useManchetteWithSpaceTimeChart.tsx b/ui-charts/src/manchette/hooks/useManchetteWithSpaceTimeChart.tsx
index 7679aae81..9589f81c8 100644
--- a/ui-charts/src/manchette/hooks/useManchetteWithSpaceTimeChart.tsx
+++ b/ui-charts/src/manchette/hooks/useManchetteWithSpaceTimeChart.tsx
@@ -2,7 +2,11 @@ import React, { type ReactNode, useCallback, useEffect, useMemo, useState } from
 
 import { sortBy, clamp } from 'lodash';
 
-import { type SpaceScale, type SpaceTimeChartProps } from '../../spaceTimeChart';
+import {
+  getCrispLineCoordinate,
+  type SpaceScale,
+  type SpaceTimeChartProps,
+} from '../../spaceTimeChart';
 import { getSpaceToPixel, spaceScalesToBinaryTree } from '../../spaceTimeChart/utils/scales';
 import type { ManchetteProps } from '../components/Manchette';
 import {
@@ -462,6 +466,11 @@ const useManchetteWithSpaceTimeChart = ({
     // Sort all contents by position:
     const allSortedContents = sortBy(allContents, 'position');
 
+    // In practice, waypoint lines are 0.5px wide only when devicePixelRatio is at least 2 (as it's
+    // implemented at the end of waypoint.css). But to get the proper alignment, we always consider
+    // it to be 0.5px wide here, because they always have this thickness SpaceTimeChart side:
+    const waypointLinesThickness = 0.5;
+
     // Iterate over all contents, to set each split section's style, and correct waypoints styles
     // accordingly:
     const finalContents: (InteractiveWaypoint | ReactNode)[] = [];
@@ -472,7 +481,7 @@ const useManchetteWithSpaceTimeChart = ({
             ...content.waypoint,
             styles: {
               position: 'absolute',
-              top: `${getSpacePixel(content.position)}px`,
+              top: `${getCrispLineCoordinate(getSpacePixel(content.position), waypointLinesThickness)}px`,
               height: `${BASE_WAYPOINT_HEIGHT}px`,
             },
           });
diff --git a/ui-charts/src/manchette/styles/waypoint.css b/ui-charts/src/manchette/styles/waypoint.css
index 8c9dbafe6..cddb3dabb 100644
--- a/ui-charts/src/manchette/styles/waypoint.css
+++ b/ui-charts/src/manchette/styles/waypoint.css
@@ -5,6 +5,7 @@
   padding-block: 3px 5px;
   width: 315px;
   position: relative;
+
   &-separator {
     position: relative;
     opacity: 0.6;
@@ -19,7 +20,6 @@
       bottom: 11px;
       left: 0;
       width: 100%;
-      height: 0.5px;
       @apply bg-grey-40;
     }
   }
@@ -92,8 +92,22 @@
     bottom: 16px;
     right: -1.625rem;
     width: 1.625rem;
-    height: 0.5px;
     opacity: 0.6;
     @apply bg-grey-40;
   }
+
+  /**
+   * Handle lines thickness, so that they are 0.5px wide only when DPR is at least 2 (since Firefox, particularly,
+   * doesn't render subpixel wide lines):
+   */
+
+  &-separator::after,
+  &::after {
+    height: 0.5px;
+    margin-bottom: -0.25px;
+
+    @media (max-resolution: 2x) {
+      height: 1px;
+    }
+  }
 }
diff --git a/ui-charts/src/spaceTimeChart/index.ts b/ui-charts/src/spaceTimeChart/index.ts
index da134ef09..3cd548884 100644
--- a/ui-charts/src/spaceTimeChart/index.ts
+++ b/ui-charts/src/spaceTimeChart/index.ts
@@ -33,3 +33,4 @@ export type {
 
 export { isPathOnScreen } from './utils/geometry';
 export { getSpaceAtTime } from './utils/scales';
+export { getCrispLineCoordinate } from './utils/canvas';