I just announced internally that after 5 years at Mozilla, and a couple as the CEO, I’ve decided to leave later this year to join Greylock Partners as a venture partner.

I’ll be in my role here at Mozilla until we conclude a successful search for a new CEO, and intend to stay involved and on the Board of Directors.

I’ll have more to say about Mozilla over the next few months as we go through transition — I’m incredibly proud of the work we’ve done over the last several years, and very optimistic about what the future holds.

And I’ll have more to say about Greylock as I move into my new role there. Venture investing is what I’ve wanted to do for quite a long time — I’ve been involved in many startups, even building an incubator a decade ago, and have interests that span enterprise, open source, and the broader web, among others. I’m incredibly excited to join an amazing team there — it’s a firm that I’ve noted to be incredibly strongly oriented towards entrepreneurs — it really matches my sensibilities as an operator extremely well.

Will be blogging and tweeting (@johnolilly) as per normal — more soon. Below is the letter I sent to everyone here at Mozilla, who I am deeply indebted to and proud of.

Everyone, As my five year anniversary at Mozilla approaches, I’ve decided that it’s time for me to move on to my next role sometime later this year. This won’t happen today or tomorrow — I expect to be here and working for several months yet, and I’m planning to stay on the Board of Directors. This is a tough note for me to write — I feel so incredibly lucky and humbled to have worked on such an amazing project, with such spectacular people, for the last few years. But I’ve always been a startup guy at heart — Mozilla was originally going to be a quick volunteer effort for me, but quickly turned into a full time job, and at the beginning of 2008 turned into the CEO job that I have now. I’ve really been missing working with startups, and want to learn how to invest in and build great new startups, so am planning to join Greylock Partners as a Venture Partner once we transition here. I’m in no rush, and the most important thing to me is to build the strongest Mozilla we can, with the best leadership possible. So my plan is to stay through that transition — we’re starting a CEO search now, and plan to do it in as transparent a way as possible — which means I’ll continue in my CEO role as normal for several more months, at least. I’ll have more to say on the transition as we figure things out more clearly, but for now, business as usual. We’ve got Firefox 4 to ship, and Firefox on multiple mobile platforms. We’ve got our web services like Weave to stand up and make available to millions of users. For now, though, I really want to communicate a deep gratitude to each of you — over the past few years we’ve done an amazing amount together, and changed the world in so many meaningful ways. 400 million users are directly touched every day by the work we’ve done so far, and many, many more are using better browsers because of our work. There are many more contributions and victories to come. John