Fractal Entertainment's SideQuest is a good example of one of these MMO Kickstarter projects that grabbed our attention. Promising a deep single-player campaign with MMO PvP and endgame elements, this browser-based game has a long list of features that make it sound unique and exciting to play. And if you read through their Kickstarter pitch, you can tell that this game will have a wicked sense of humor.
The best news is that Fractal Entertainment seems to be willing to make this game even if their Kickstarter campaign doesn't meet its goal, but the extra funding will be going towards making it bigger and better than it already will be.
So check out their Kickstarter page, thumb through the rewards, and browse the game's features. This might just be the browser-based game you've been looking for.