You might well be right, but I, along with lots of other firefox users run extensions like NoScript which blocks 3rd party javascript unless explicitly whitelisted, so I expect a much higher proportion of firefox users probably don't show up on analytics packages (which is how statcounter stats are generated). DuckDuckGo Privacy essentials plugin also blocks statcounter, as I'm sure do many other privacy related plugins.

Even if you are a firefox user who doesn't use third party plugins, firefox itself will block statcounter if you have enhanced tracking protection turned on. I couldn't find a similar setting in Chrome.