To get clicking on the blank area to open a new tab, you have to extract omni.ja (which is a ZIP file with an intentionally corrupted header, so only a few unzip tools can actually extract it), and patch some of the UI code, then recompress it. Guide here: http://board.byuu.org/viewtopi...
The problem is, no matter how much patching you do, it's not really possible to get Seamonkey to behave decently. There's just so many little annoyances.
I've never been able to get Flash to work in Seamonkey on Windows no matter what I've tried. Fullscreen video doesn't actually go fullscreen, it just opens a slightly larger window inside your browser. F11 browser fullscreen mode doesn't auto-hide all the navigation controls. Trying to add an exemption to your popup blocker is damn near impossible
I'm just holding out on Firefox 28 for as long as possible, and hoping someone makes a decent Webkit or Gecko browser UI for Linux. If it gets too bad and FF28 is too old, I'll have to start looking into making my own. And just to mention it, Classic Theme Restorer looks absolutely hideous under Linux with Xfce/Clearlooks. It's clearly designed for Windows, with OS X and Linux as an afterthought. Half the UI options don't even have apply to Linux or just plain don't work, and the other half result in very extreme rendering bugs.