Since I work on Chromium, I kind of care about this... We're still an open source project. We still take a lot of external contributions, as far as I know.
Can you point to concrete cases where Chromium has not taken contributions (without giving a good reason, that is)?
It's probably hard to point out a specific case, but I think the biggest objection is that most Chromium developers have a tight connection with Google (if not employees anyway). They have mostly incentive to keep their employer happy. Google keeps the shareholders happy and they just want more money. (At the cost of privacy or open standards for example). Now this may be a simplified view, since this may apply to any company. However, Mozilla has some core principles they really try to stick to.
The team works really hard both on privacy and on open standards. But let's set that aside for a moment: There are many other companies contributing as well. (Opera, Samsung, Intel pop out when I just browse through the commit logs, but I'm sure I'm missing more).
And you as an individual, are free to contribute as well. We welcome OSS devs who want to help make Chrome better. Send me a ping if you ever get stuck, should you choose to contribute.
Yes, the project does not accept all changes. We can't, and no OSS project can. Some don't make sense ("Render all text blinking!" ;), some don't work for what the general idea for Chromium is ("Let's remove JS!"). But in general, the team tries to be accommodating when somebody wants to land a change.
I can understand when people say "Hey, Mozilla aligns more with what I want, I'll contribute there". It's awesome. You should work on something you believe in, and I'm glad you've found a project that works for you.
But Chromium is certainly happy to accept contributions, contrary to what the OP said.
Can you point to concrete cases where Chromium has not taken contributions (without giving a good reason, that is)?