[mgse]

"If you have extensive and current open source contributions, for most people it means ... you're violating your employer's contract terms."

Bingo (at least for me). Both companies I've worked for require you to submit a proposal to an open source review board for approval. I went through the process at my previous job and approximately 2 months later I was given the go-ahead. Not worth it.

[acdha]

These days it often can mean quality bug reports. Many popular open source projects are more responsive to pull requests than simple tickets, so it's entirely possible to have a Github account which is used only for support with opensource projects which your employer relies on.