I switch between Chrome and Firefox routinely on my Mac whenever something irks me about one particular browser. They look so similar that the only way I can tell the difference is by looking at the status bar at the application name. Today I saw a screenshot of Opera and was blown away at how similar all three are.
###Similar, but different
There are lots of examples of other products that come to mind that closely resemble competitors. Operating systems use the same type of task bars where they have an entry button, a list of open applications and then an area for frequently viewed items like clock and battery life.
This happens outside of the software market with actual physical products, see DVD players and phones.
But after I look at both dvd players and operating systems, they do not closely resemble each other as internet browsers do.
###Human interface guidelines
Often manufacturers of an application ecosystem create what is called a Human Interface Guideline to document how all applications should look and feel. Both IOS and Android publish such a document and developers stick to it as much as possible.
But again that is not the case for internet browsers as they do not share the same manufacturer.
On the big screen, movies that share the same plot are released the same year are so common that there is a Wikipedia entry on it. See Twin Films.
A reddit user recently put together a good comparison on Imgur listing out the popular Twin Films
###Principle of least astonishment
Or did we as developers and users of internet browsers get so used to thinking of how an internet browser should be assembled that over time all the components were placed in similar positions.
In the study of usability this is known as following the Principle of least astonishment
It is interesting to note that I can not find any lawsuits that have come up for internet browsers, but see them all the time for phone makers. Does anybody else have any other ideas?