Extensions download like files in dev channel

Whenever I click any "Install extension" links for Chrome, Chrome tries to route it like a normal file. It asks me if I want to download it like any other file, instead of prompting me to install it. If I open the file with Chrome (from Windows Explorer), it does the same thing.
I'm using Dev channel version 4.0.223.11.
If I go to chrome://extensions/ I can install unpacked extensions, but they don't work, and they uninstall after I close Chrome.
This is the only reason I don't use chrome. I really need to install Xmarks for Chrome, or at least sync Google Bookmarks with Xmarks automatically.