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Maybe Firefox usage statistics could be distorted, because of its various mechanisms of blocking trackers.

It would surprise me greatly if Firefox were sending invalid User-Agent headers.

User-Agent headers are mandatory; and it would be counterproductive for everybody, including Mozilla, if Firefox were sending invalid User-Agent headers.

For years I sent a blank UA string. It worked surprisingly well until about 2010. Only real issue was some Tomcat servers would just barf out stack traces.

UA switcher is a pretty popular addon in the Mozilla ecosystem. So it may well be more popular than UA stats alone can surmise. (Though probably not enough to matter to businesses too lazy to test anything besides the top two.)

According to Mozilla only like a third of all Firefox users have installed any add-on at all. So multiply the number by 150% and you have the highest possible Firefox usage rate.

Similar experience. :-P It didn't seem to be mandatory until suddenly it was.

> Maybe Firefox usage statistics could be distorted, because of its various mechanisms of blocking trackers.

I didn't think that that blocked the user-agent header. But I guess I could be wrong.

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