I feel one issue is that the people who are Firefox power users are also disabling telemetry, so the developers aren't getting any usage data from the people who care the most about Firefox. So the only usage data they receive is from the normal user, who want different things and use the browser differently.
It's not about telemetry, most people just use the data to support whatever they want.
For example, firefox users of all sorts customized things. People loved it. Themes, plug-ins, add-ons.
Firefox devs consistently fail to realize that "configurability" is a category, not "this tiny configurable thing".
So they've removed configurable after configurable option, each option only having .1% market share usage or what not, not considering that overall... they've now alienated 20% of their user base.
Telemetry shows them a tiny percentage for each feature, but it is the collective feature set which matters.
And that has a cumulative effect. 20% upset users, all saying "Don't use firefox!", doesn't help.
Then they add useless, in your face, obtrusive and annoying features, and people scramble to diaable them.
"Oh so sorry, disable that?!". Sometimes years go by, and all the instantly closed bug reports add up, and they finally relent, fix it. Of course, everyone who cared is now gone, and will never come back, and now campaigns against firefox.
Just like the infamous tab detach issue, which took half a decade to resolve, by finally adding an about:config option to turn that off.
And who cares for telemetry, when hundreds of users complain, and bugs are ignored, or just hostile closed?
