1. the largest part of the work on the "major rewrite" - do you mean quantum or servo? If the former, most of the bits we really care about will get shipped on Nov. 14th, and some other things like webrender will get shipped over the winter.
If you mean servo, you're right, that is a longer-term strategic project, but has recently provide useful as a source for innovation in Gecko with things like stylo and webrender, and especially Rust's capabilities as a language.
2. Mozilla is self-funded and has a very different governance model than perhaps you're used to - we are a US Corp ( and subsidiaries ) owned entirely by a US-based Not-for-profit.
...and, yes there is a legacy problem with old code bases, but one trade-off for interns, contributors, junior developers is that you get to make an impact on a codebase used in a commercial project by hundreds of millions of people. Terrible tools written in anger in 2003 are still in use, sure, and terrible architectural decisions have been made, re-made, then made again over the years. It's the kind of messy any codebase eventually gets to.
This codebase still has life in it though, and the proof is in how far Gecko has come in the last year. Go run Nightly for a bit, compare it to Chrome or current Firefox. It's a big deal.
Jan Odvarko, the author of this post, is a Mozilla employee working on Firebug and related projects. He has worked for Mozilla for 4+ years and is paid to maintain / improve Firebug.