I find the crowdsourced data at levels.fyi to be a good reality check on what dev compensation is like at large tech companies.

Let's take three others that make well-known desktop browsers: https://www.levels.fyi/?compare=Apple,Google,Microsoft&track...

According to that data, senior developers at Apple (ICT4), Google (L5) and Microsoft (64) make on average $320k, $352k, and $225k. Their fully-loaded costs (benefits, payroll taxes, office space, etc) to the company will of course be even higher.

These are examples of peer companies Mozilla is competing against for employees. As I explained at https://news.ycombinator.com/item?id=24138083 , Mozilla does not try to attract people solely via compensation. However, you can only offer so much less before you're no longer able to hire and retain the talent you need.