–Overlapping of Layout and Elements.
— Rendering Issues.
— Element out of Bounds or exceeding its container or not displayed.
— Inconsistency of third party plugins.
— Different Font Sizes across various browsers.
— Changing size of Elements across browsers.
— Alignment Issues.
— HTML Errors and broken pages.
— Browser Bugs Little known errors cause big problems.
— Inconsistent Popups and other message boxes across browsers.
— Page Loading time across browsers – are a few worth a mention.