The CEOs salary has almost zero affect on Firefox's market share.
That decline can be explained relatively simply by two things.
One, people are increasing using mobile devices and very very rarely do they install another browser so they are using Chrome on Android and Safari on Apple devices.
Two, Google was/is using Google dot com to promote chrome. That is not something Mozilla could ever replicate.
Then there is the other bit where Mozilla tries to diversify their revenue sources and the faithful skewer them for it and tell them "just work on Firefox" when it is clear the market is unwilling to pay for a browser at all.
If you look at it from an incentive view point you have to pay people more to Capitan a sinking ship.
Also worth noting is that market share may or may not be relevant. Android has a higher market share world wide compared to Apple, however Apple users generate more revenue.
All this to say that the op graph is at best an incomplete picture of things designed to rile up people who lack critical thinking.