At one point, Firefox (3.5 specifically) was #1, for a brief moment:

> Between mid-December 2009 and February 2010, Firefox 3.5 was the most popular browser (when counting individual browser versions) according to StatCounter, and as of February 2010 was one of the top 3 browser versions according to Net Applications. Both milestones involved passing Internet Explorer 7, which previously held the No. 1 and No. 3 spots in popularity according to StatCounter and Net Applications, respectively - https://en.wikipedia.org/wiki/Firefox_3.5

Then Chrome appeared and flattened both IE and Firefox.

Millions of people use it. What's the latest usage number? 5% or something?

There's 5 billion people on the internet. 5% of that is 250 million.

Some companies would kill for user numbers like that. Hell, some would slaughter entire villages.

Define taking off then. Everyone knows Firefox and some people even like it