I'm sure Mozilla feels very precarious getting such a huge chunk of money from a single source. But:

- Mozilla isn't a company, it's a non-profit (this deal was done by Mozilla Corp, yes, but that's a wholly owned branch of the foundation). Reducing their reliance on Google for cash is never going to be Mozilla's aim as a whole.

- Three years is a hell of a long time. When the last deal was negotiated, there was no Bing, and no Chrome. The world was a very different place. No matter how good their strategy is, it's going to be a terrible one for the world in 3 years time.

- The interests of the Mozilla foundation and Google are broadly aligned - they both care about an open, free web. That's a rare thing to find in large industry players these days.