> Firefox market share has been going downhill for most of my life

Firefox market shares are the best of any non OEM browser[1] and is beating competition from a number of OEM browser (like Samsung's one on mobile) and is fairly competitive compared to the desktop version of Safari (only 1% below on desktop market share).

Yes market share have been going downhill but mostly because they were abnormaly high for something that doesn't ship with the computer in late 90's early 2000's due to:

- the inertia of being born from the ashes of Netscape, which was the default browser at the beginning of eternal september.

- it had its highest market share at a time when its strongest competition was Internet Explorer: a magnet for malwares.

So its market shares are quite good actually. Note that Opera (and now Vivaldi) never got close despite being appreciated by many.

[1] yes it comes with many linux distro but it is sold with virtually zero device.