When I went professional with my web development (2009) I can remember the in-the-know people were actively advocating for feature detection, but it was still common practice even in 2010 to add IE-specific support using conditional comments to load stylesheets with fixes for a known IE version.
You probably still have nightmares of these:
https://msdn.microsoft.com/en-us/library/ms537512(v=vs.85).a...
On the way to 2012 it became clear once Microsoft said they never intended to let IE announce itself as IE in the future that the game was finally over for UA sniffing. The funniest part was I still remember the MS fanboy blog post that was saying how wonderful it would be that future versions of IE would identify itself as not IE, and how this would make the world a better place. :P
