"Firefox Market share revisited" by former Mozilla CTO

[Brummelchen]

me again - andreas gal is not wrong as he pointed out the ADI stats. those are complete different from stats like statcounter
https://gs.statcounter.com/browser-market-share

ADI contains downloads and installations and sessions, while statcounter collect real world usage, for me complete different. i would trust more the data from statcounter because i have several firefox installations but only use one - if i use, but my current used browser in most cases is chromium. so i have fed ADI stats less that statcounter.

[Tomatoshadow2]

Very well said Brummelchen!

[trustjmh]

The I stands for installation, i.e. a profile on hard disk. Just like an art installation maybe contents of a room in some gallery.
Active means Firefox was ran with that profile and it contacted Mozilla server. Profiles record time so this only happens daily.
You can't compare the value to any other browser as there could be discrepancy in the way it is gathered. In all likelihood it is stable to compare to the value from years ago to the current one and get a measure of absolute growth or shrinkage.

The statcounter link shows about the same as ADI. (Assuming there has been no change in market size.)

Drop of 25-30% in last year
5.93/8.31 vs 74/102 (these are about midweek values that I have seen in the dashboard in the past.)