Use <button/> rather than <i/> for tab buttons.

packages/rocketchat-ui-flextab/flex-tab/flexTabBar.html

 <template name="flexTabBar">
 	{{#each buttons}}
 		<div class="tab-button {{active}} {{visible}}" title="{{title}}">
-			<i class="{{icon}}" aria-label="{{title}}" role="button" tabindex="0"></i>
+			<button aria-label="{{title}}"><i class="{{icon}}"></i></button>
 		</div>
 	{{/each}}
 </template>