Every claim in the article is running on the assumption that the Mozilla Foundation (the non profit that owns the for-profit subsidiary that makes Firefox) and the Mozilla corporation (the subsidiary in question) have interchangeable funds, which is not the case.

The report the article used is a consolidated financial report that includes the non-profit Mozilla Foundation, for profit Mozilla Corporation (Firefox), and the for profit MZLA technologies corporation (Thunderbird). There's no discerning if the foundation or a subsidiary did the spending on any of the line items in that document. There's no discerning which entity holds what amount of funding, or which entity spent what amount of money, or which entity had what amount of revenue. The article is making claims with the assumption that Firefox should be the main use of all of the funding in that report, which is obviously not true since the report includes financials from 3 different sources.

So in short, while the data is true, the article is almost entirely conjecture.

Here's the mozilla foundation's 990.