[nitwit005]

You have to be realistic about what you expect here. Suppose it takes you 1/100th of the time it took them to write the code to understand it. Some of these projects have had hundreds of people working on them for years. It may take you months to get a basic grasp of things.

At my current company it often takes 6 months for experienced people to become productive, and that's with a helping hand.

IDEs are nice, but grep remains the best tool. You tend to need to find things in XML files and config as well.

[jondubois]

It depends heavily on code quality.

In general, I think that high quality code attracts high quality pull requests. That's because high quality code is easy to understand and easy to change because the core structure of the code is fundamentally sound and well suited to the problem that it is solving.