Comment by denormalfloat

There are wrong reasons to sniff the UA string, and less wrong reasons. If a Browser has a bug that gets fixed in later versions, sites have to sniff the UA string to do the right thing. For example, a browser bug may cause people to see an error, and the they are using an old version of the browser. The right thing to do is to upgrade, but how to tell? When you are subject to the bugs of some other code, and which are skewed across different versions of the software, the most reasonable way to work around it is by UA sniffing.