dashboard: help: add note about other browser extensions impacting pe…

…rformance

dashboard/dashboard.html

@@ -445,6 +445,7 @@
 			</p>
 			<ul>
 				<li>If your ad blocker is enabled for this domain, you will see slower performance, and some URLs will not be displayed.</li>
+				<li>Performance may be impacted by other browser extensions that watch the DOM. Sometimes the offending extension can be found using the profiler in the DevTools 'Performance' tab.</li>
 				<li>A custom context menu is shown when right-clicking URLs in the log windows below. It can be disabled by adding <kbd><span class="url-q-or-amp">?</span>contextMenu=0</kbd> to the dashboard URL. Firefox users: if you see both the normal and custom context menu, make sure <code>dom.event.contextmenu.enabled</code> is set to <code>true</code> in <code>about:config</code>.</li>
 				<li>To change the font used on this page, customize the sans-serif font in your browser's font settings.</li>
 			</ul>