* Vinod Khosla, Accel's Breyer to join board as observers
* Funding to help RockMelt grow, develop partnerships
* Customers use browser service average of 6.5 hours daily
SAN FRANCISCO, June 28 (Reuters) - RockMelt, a Web browser that integrates Facebook and other social media, reeled in two more Silicon Valley heavy hitters in a new $30 million round of financing.
Accel Partners and Khosla Partners joined existing investor Andreesen Horowitz in this latest round, the company and investors said. Accel's Jim Breyer and Khosla's Vinod Khosla will take observer roles on RockMelt's board.
Rockmelt lets Facebook users send messages from their main browswer screens and signals when there is news a reader wants -- a new Tweet or an update on a favorite website. The idea is to make the Web browser, increasingly the portal for applications as well as Web surfing, a one-stop shop for people hooked on social media.
Many of these features are the result of a partnership of RockMelt and Facebook, which is also backed by Andreesen Horowitz.
Breyer called a browser built to optimize social media "a compelling opportunity."
The company helps to use better timing and execution to avoid the fate of Flock, a browser that integrated social media but never achieved a critical mass of users, said RockMelt co-founder and Chief Technology Officer Tim Howes. Social-gaming company Zynga bought Flock earlier this year, and then announced in April it would discontinue support of the browser.
"They were just simply too early," said Marc Andreesen of Andreesen Horowitz, one of RockMelt's early backers, about Flock.
The cash will allow the roughly 40-person company to grow faster and develop partnerships in areas such as music, e-commerce and gaming, company executives said.
RockMelt's goal is to amass "hundreds of millions" of users as use of social media like Twitter and Facebook becomes increasingly pervasive, but its executives declined to specify a time frame or be more specific about numbers.
Currently, about 1 million customers have tried RockMelt, of which several hundred thousand are active users, said RockMelt Chief Executive and co-founder Eric Vishria and co-founder and chief technology officer Howes.
The average person uses it for 6.5 hours a day, and more than half of users are 24 years old or younger, according to the two co-founders.
The company previously raised $8.2 million in September 2009 and $1.7 million in an angel round in February 2009. The company declined to give its latest valuation.
RockMelt is based on Chromium, the same technology as Google's (GOOG.O) Chrome browser. On Tuesday, Google announced a Facebook competitor called GooglePlus. (Editing by Steve Orlofsky)