Two or three years ago I "found" a new web browser called Phoenix. It was based on the Mozilla rendering engine (Gecko), but was much smaller. I gave it a shot. I liked it, but it wasn't enough for me, so I uninstalled and forgot about it.
Some time later, I saw another new browser, also based on Mozilla. This one was called Firebird. Only after downloading and reading about it, I found out this was actually a new name for Phoenix. This version was much better (as far I as remember) than the Phoenix, so I kept it.
I updated Firebird with every minor version. One upgrade suddenly changed the name to... Firefox. Whatever. Firefox was a really good browser, so I stopped using MSIE (*).
I followed Firefox with anticipation through all versions. I was really happy when version 1.0 was out, and installed it on every computer I go to (work computers, friends computers, etc).
And now - 50 million is a real milestone. Wow.
Congratulations, Mozilla developers! Thank you, and keep up the good work!
(*) Except for annoying sites that won't render correctly in non-IE browsers.