diff --git a/e2e-tests/tests/selection/right-click-selection.spec.js b/e2e-tests/tests/selection/right-click-selection.spec.js
new file mode 100644
index 0000000000..c8f20731fc
--- /dev/null
+++ b/e2e-tests/tests/selection/right-click-selection.spec.js
@@ -0,0 +1,42 @@
+import { test, expect } from '@playwright/test';
+import { goToPageAndWaitForEditor } from '../helpers.js';
+
+// TODO: Add Firefox to playwright.config.js projects to catch Firefox-specific regressions.
+// This test was added for SD-1623 where Firefox clears selection on right-click mousedown
+// when preventDefault() is called, unlike Chrome/Safari.
+test.describe('Right-click selection preservation', () => {
+  test('preserves text selection after right-click @SD-1623', async ({ page }) => {
+    await goToPageAndWaitForEditor(page);
+
+    const editor = page.locator('div.super-editor').first();
+    await editor.click();
+
+    // Type some text to select
+    const testText = 'Hello World';
+    await page.keyboard.type(testText);
+
+    // Select all the text we just typed
+    await page.keyboard.press('ControlOrMeta+a');
+
+    // Verify text is selected before right-click
+    const selectionBefore = await page.evaluate(() => window.getSelection()?.toString());
+    expect(selectionBefore).toContain(testText);
+
+    // Right-click on the selected text
+    const textElement = editor.getByText(testText);
+    await textElement.click({ button: 'right' });
+
+    // Wait a moment for the selection handlers to run
+    await page.waitForTimeout(100);
+
+    // Verify selection is preserved - check for either:
+    // 1. Native selection still present, OR
+    // 2. Visual selection decoration applied (sd-custom-selection class)
+    const selectionAfter = await page.evaluate(() => window.getSelection()?.toString());
+    const hasVisualSelection = await editor.locator('.sd-custom-selection').count();
+
+    // Either the native selection should be preserved OR the visual decoration should be shown
+    const isSelectionPreserved = selectionAfter.includes(testText) || hasVisualSelection > 0;
+    expect(isSelectionPreserved).toBe(true);
+  });
+});
diff --git a/packages/super-editor/src/extensions/custom-selection/custom-selection.js b/packages/super-editor/src/extensions/custom-selection/custom-selection.js
index 1695b762a8..cd72bd1a60 100644
--- a/packages/super-editor/src/extensions/custom-selection/custom-selection.js
+++ b/packages/super-editor/src/extensions/custom-selection/custom-selection.js
@@ -187,7 +187,9 @@ export const CustomSelection = Extension.create({
                 return false;
               }
 
-              event.preventDefault(); // Prevent default right-click behavior
+              // Note: Do NOT call event.preventDefault() here.
+              // Firefox clears native selection when preventDefault is called on mousedown.
+              // The contextmenu handler already prevents the native menu.
               const { selection } = view.state;
               if (!selection.empty) {
                 // Ensure selection stays visible for right-click/context menu
diff --git a/packages/super-editor/src/extensions/custom-selection/custom-selection.test.js b/packages/super-editor/src/extensions/custom-selection/custom-selection.test.js
index 0b085db526..3c8e3e678e 100644
--- a/packages/super-editor/src/extensions/custom-selection/custom-selection.test.js
+++ b/packages/super-editor/src/extensions/custom-selection/custom-selection.test.js
@@ -267,6 +267,32 @@ describe('CustomSelection plugin', () => {
     expect(firstDeco?.to).toBe(6);
   });
 
+  it('does not call preventDefault on right-click mousedown to preserve Firefox selection', () => {
+    const { plugin, view, editor } = createEnvironment();
+
+    const mouseDownEvent = {
+      button: 2,
+      preventDefault: vi.fn(),
+      target: editor.options.element,
+      type: 'mousedown',
+    };
+
+    plugin.props.handleDOMEvents.mousedown(view, mouseDownEvent);
+
+    // preventDefault should NOT be called for right-click mousedown
+    // because Firefox clears native selection when preventDefault is called
+    expect(mouseDownEvent.preventDefault).not.toHaveBeenCalled();
+
+    // But selection should still be preserved in plugin state
+    expect(view.dispatch).toHaveBeenCalled();
+    const dispatchedTr = view.dispatch.mock.calls[0][0];
+    expect(dispatchedTr.getMeta(CustomSelectionPluginKey)).toMatchObject({
+      focused: true,
+      preservedSelection: expect.any(Object),
+      showVisualSelection: true,
+    });
+  });
+
   it('keeps selection visible when toolbar elements retain focus', () => {
     const { plugin, view, editor } = createEnvironment();