Many of us who use the internet for work and leisure come to feel that we couldn't live without it. The web opens up the world, but does it also harbour fundamental threats to our privacy, security and autonomy? Can we trust the tech companies who shape our relationship with the internet? Stephen Sackur speaks to Mitchell Baker, a Silicon Valley pioneer and boss of the not-for-profit Mozilla Corporation, best known for the Firefox web browser. Is her open-source collaborative model of web innovation being overwhelmed by the power of the profit motive?