SeaMonkey 2.10 contains the following major changes relative to SeaMonkey 2.9:

SeaMonkey-specific changes

• The domain name is highlighted in the location bar by default now, configurable in Preferences.
• The amount of tabs to be restored concurrently can be configured in Preferences now.
• News username and password auth dialogs have been combined and show for which server the prompt is now.

Mozilla platform changes

• The new minimum supported Windows version is now XP SP2, Windows 2000 support has been dropped.
• The SPDY protocol now enabled by default for faster browsing on supported sites
• The column-fill CSS property has been implemented.
• Experimental support for ECMAScript 6 Map and Set objects has been implemented.
• Support for the CSS3 background-position property extended syntax has been added.
• The :invalid pseudo-class can now be applied to the <form> element.
• The CSS turn <angle> unit is now supported.
• Fixed several stability issues.