Nice timeline, though I have some doubts about its accuracy / completeness. It makes it look as if Safari predates Firefox, but I remember that I had been using Firefox (then still called Phoenix) as early as 2002 - 2 years before the 1.0 launch.
Also notably absent is the Mozilla suite that predated Firefox.
Looks pretty but isn't very practical. E.g. why is the 'webfonts' label way off the screen from the point it is first implemented? How do I see what features were implemented in a particular browser version? Why is there a massive text banner in front of the screen shots of different browser versions?
I think it's supposed to trace a line between the first implementation of each feature in each browser. Where the colored lines intersect a dot, that's where the feature was implemented. The rest is just flair.
The most fascinating part about this timeline, for me, is that it's so short. Feels like forever ago I was using Netscape on Windows 95, but it really wasn't. It's come so far in such a short amount of time.
When looking at the screenshot slides, clicking on the top right corner of the image (near where the 'x' is in most of the screenshots) actually closes the slideshow. This is a nice little usability detail.
Also notably absent is the Mozilla suite that predated Firefox.