diff --git a/webextensions/common/Tab.js b/webextensions/common/Tab.js
index 1b4fae0ce..948109c39 100644
--- a/webextensions/common/Tab.js
+++ b/webextensions/common/Tab.js
@@ -14,6 +14,7 @@ import {
   mapAndFilter,
   mapAndFilterUniq,
   toLines,
+  sanitizeForHTMLText,
   sanitizeForRegExpSource,
   isNewTabCommandTab,
   isFirefoxViewTab,
@@ -608,6 +609,34 @@ export default class Tab {
     return tooltip.join('\n');
   }
 
+  generateTooltipHtml() {
+    return this.cookieStoreName ?
+      `<span class="title-line"
+            ><span class="title"
+                  >${sanitizeForHTMLText(this.tab.title)}</span
+            ><span class="cookieStoreName"
+                  >${sanitizeForHTMLText(this.cookieStoreName)}</span></span>` :
+      `<span class="title-line"
+            ><span class="title"
+                  >${sanitizeForHTMLText(this.tab.title)}</span></span>`;
+  }
+
+  generateTooltipHtmlWithDescendants() {
+    return `<ul>${this.generateTooltipHtmlWithDescendantsInternal()}</ul>`;
+  }
+  generateTooltipHtmlWithDescendantsInternal() {
+    let tooltip = `<li>${this.generateTooltipHtml()}`;
+    const children = [];
+    for (const child of this.children) {
+      if (!child)
+        continue;
+      children.push(child.$TST.generateTooltipHtmlWithDescendantsInternal());
+    }
+    if (children.length > 0)
+      tooltip += `<ul>${children.join('')}</ul>`;
+    return `${tooltip}</li>`;
+  }
+
   registerTooltipText(ownerId, text, isHighPriority = false) {
     if (isHighPriority) {
       this.highPriorityTooltipTexts.set(ownerId, text);
diff --git a/webextensions/resources/tab-preview-frame.js b/webextensions/resources/tab-preview-frame.js
index 59d0183b2..e5eb32a9d 100644
--- a/webextensions/resources/tab-preview-frame.js
+++ b/webextensions/resources/tab-preview-frame.js
@@ -178,6 +178,33 @@ try{
     .updating {
       visibility: hidden;
     }
+
+
+    /* tree */
+    .tab-preview-tooltip-text ul,
+    .tab-preview-tooltip-text ul ul {
+      margin: 0 0 0 1em;
+      padding: 0;
+      list-style: disc;
+    }
+
+    .tab-preview-tooltip-text .title-line {
+      display: flex;
+      flex-direction: row;
+      max-width: 100%;
+      white-space: nowrap;
+    }
+    .tab-preview-tooltip-text .title-line .title {
+      overflow: hidden;
+      text-overflow: ellipsis;
+    }
+    .tab-preview-tooltip-text .title-line .cookieStoreName {
+      display: flex;
+      margin-left: 1ch;
+    }
+    .tab-preview-tooltip-text .title-line .cookieStoreName::before {
+      content: "- ";
+    }
   `;
   document.head.appendChild(style);
 
@@ -270,7 +297,7 @@ function createPanel() {
   return panel;
 }
 
-function updatePanel({ tabId, title, url, tooltipText, hasPreview, previewURL, tabRect, offsetTop, align, scale } = {}) {
+function updatePanel({ tabId, title, url, tooltipText, tooltipHtml, hasPreview, previewURL, tabRect, offsetTop, align, scale } = {}) {
   if (!panel)
     return;
 
@@ -297,12 +324,12 @@ function updatePanel({ tabId, title, url, tooltipText, hasPreview, previewURL, t
   const titleElement = panel.querySelector('.tab-preview-title');
   const urlElement = panel.querySelector('.tab-preview-url');
   const tooltipTextElement = panel.querySelector('.tab-preview-tooltip-text');
-  if (typeof tooltipText == 'string') {
+  if (typeof tooltipHtml == 'string') {
     if (typeof title == 'string' &&
         tooltipText != title) {
       titleElement.classList.add('hidden');
       urlElement.classList.add('hidden');
-      tooltipTextElement.textContent = tooltipText;
+      tooltipTextElement.innerHTML = tooltipHtml;
       tooltipTextElement.classList.remove('hidden');
       panel.classList.add('extended');
     }
diff --git a/webextensions/sidebar/components/TabElement.js b/webextensions/sidebar/components/TabElement.js
index 238d19b74..8a22a778c 100644
--- a/webextensions/sidebar/components/TabElement.js
+++ b/webextensions/sidebar/components/TabElement.js
@@ -5,7 +5,8 @@
 */
 
 import {
-  configs
+  configs,
+  sanitizeForHTMLText,
 } from '/common/common.js';
 import * as Constants from '/common/constants.js';
 import * as TabsStore from '/common/tabs-store.js';
@@ -409,6 +410,8 @@ windowId = ${tab.windowId}
 
     this.tooltip                = this.$TST.generateTooltipText();
     this.tooltipWithDescendants = this.$TST.generateTooltipTextWithDescendants();
+    this.tooltipHtml            = this.$TST.generateTooltipHtml();
+    this.tooltipHtmlWithDescendants = this.$TST.generateTooltipHtmlWithDescendants();
 
     const tooltipText = configs.tabPreviewTooltip ?
       null :
@@ -429,7 +432,7 @@ windowId = ${tab.windowId}
     const highPriorityTooltipText = this.$TST.getHighPriorityTooltipText();
     if (typeof highPriorityTooltipText == 'string') {
       if (highPriorityTooltipText)
-        return this.tooltip;
+        return highPriorityTooltipText;
 
       return null;
     }
@@ -455,6 +458,42 @@ windowId = ${tab.windowId}
     return tooltip;
   }
 
+  get appliedTooltipHtml() {
+    if (configs.showCollapsedDescendantsByTooltip &&
+        this.$TST.subtreeCollapsed &&
+        this.$TST.hasChild) {
+      return this.tooltipHtmlWithDescendants;
+    }
+
+    const highPriorityTooltipText = this.$TST.getHighPriorityTooltipText();
+    if (typeof highPriorityTooltipText == 'string') {
+      if (highPriorityTooltipText)
+        return sanitizeForHTMLText(highPriorityTooltipText);
+
+      return null;
+    }
+
+    let tooltip = null;
+
+    const tab = this.$TST.tab;
+    if (this.classList.contains('faviconized') ||
+        this.overflow ||
+        this.tooltip != tab.title)
+      tooltip = this.tooltipHtml;
+    else
+      tooltip = null;
+
+    const lowPriorityTooltipText = this.$TST.getLowPriorityTooltipText();
+    if (typeof lowPriorityTooltipText == 'string' &&
+        !this.getAttribute('title')) {
+      if (lowPriorityTooltipText)
+        tooltip = sanitizeForHTMLText(lowPriorityTooltipText);
+      else
+        tooltip = null;
+    }
+    return tooltip;
+  }
+
   _initExtraItemsContainers() {
     if (!this.extraItemsContainerIndentRoot) {
       this.extraItemsContainerIndentRoot = this.querySelector(`.${Constants.kEXTRA_ITEMS_CONTAINER}.indent`).attachShadow({ mode: 'open' });
diff --git a/webextensions/sidebar/tab-preview-tooltip.js b/webextensions/sidebar/tab-preview-tooltip.js
index f81a10667..16ca9faca 100644
--- a/webextensions/sidebar/tab-preview-tooltip.js
+++ b/webextensions/sidebar/tab-preview-tooltip.js
@@ -303,6 +303,7 @@ async function onTabSubstanceEnter(event) {
 
   hoveringTabIds.add(event.target.tab.id);
   const tooltipText = event.target.appliedTooltipText;
+  const tooltipHtml = event.target.appliedTooltipHtml;
 
   const targetTabId = CUSTOM_PANEL_AVAILABLE_URLS_MATCHER.test(activeTab.url) ?
     activeTab.id :
@@ -349,6 +350,7 @@ async function onTabSubstanceEnter(event) {
     title: event.target.tab.title,
     url,
     tooltipText,
+    tooltipHtml,
     hasPreview,
     timestamp: startAt, // Don't call Date.now() here, because it can become larger than the timestamp on mouseleave.
     canRetry: !!targetTabId,