Browser-based mining, as its name suggests, is a method of cryptocurrency mining that happens inside a browser and is implemented using scripting language. This is different compared to the more widely known file-based cryptocurrency mining approach which involves downloading and running a dedicated executable file.
Even though it was possible at that time to mine for Bitcoin via BitcoinPlus.com, the reality of the situation was that it was largely a futile exercise. The reward was minuscule compared to the amount of mining power and electricity required. Of course, this was back in the days before Bitcoin prices shot through the roof—in June 2011, Bitcoin reached the then lofty heights of almost US$30.