There's a very interesting pattern in the data if you look back from 2016-05 to 2018-04 (chart has 24 month limit). Each April and October shows an appreciable drop in Firefox market share. This tells me that the Firefox desktop/laptop we are losing are on Linux and decide to switch to another browser when they upgrade their (probably Ubuntu based) disto.

I myself run Firefox on Xubuntu but stick to the LTS releaaes. The biggest impediment from switching from Chrome to Firefox was being familiar with the Dev Tools. One day I just did it and the change wasn't as big a deal as I thought it to be.

We really need to keep Firefox alive, it's our best, free-est option. With Microsoft replacing Edge with a Chrome-based browser this is as important as ever.