General
- ChatZilla has been updated to a newer version (Bug 324439)
- [Mac] Menus and menu popups use more native styling (Bug 301105)
- [Linux] When launching SeaMonkey, already-running instances are detected (Bug 122698)

Browser
- A warning page is now shown before displaying about:config (Bug 339720)
- When you visit a secure site, the URL bar changes color to turns make security status more visible (Bug 335113)
- When using keyword URLs, it is no longer necessary to type "keyword:" (typing "keyword:" will no longer work). Just type the keyword name (Bug 337339)
- You can now drop URLs and bookmarks between existing tabs, which will result in a new tab being created where you dropped the URL (Bug 324591)
- When hovering on a tab, the tooltip now displays a preview of the tab's contents (Bug 315207)
- The search sidebar now behaves better (Bug 252802)
- The bookmarks menu and personal toolbar folder overflow menu now have context menus (Bug 50504)

Mail & Newsgroups
- Message labeling has been superseded by tagging, which provides much more than the original 5 labels and comes with new preferences (Bug 342560 and others)
- The preferences for junk mail have been modified to accommodate behavior changes (Bug 335846)
- Improved phishing detection (Bug 326082 and others)
- [Linux, Mac] New mail notification has been improved (Bug 327613, 305384, and others)