Answer: Detect user agent
Step-by-step explanation:
Although is not recommended to use this method, as is better for usability and accessibility the implementation of feature detection and Progressive enhancement in the modern web, it is possible to detect the browser by sniffing the user agent string to detect which browser is being used. The part you would look to distinguish each browser is found in the Rendering Engine and the values you will get are: Gecko, Webkit, Presto, Blink.