There are only a few important extensions. just remember them.
> Computers are supposed to work for people, not the other way around.
Extensions are not for average computer users. They have icons and filenames. Windows also hides extensions by default.
.xpi is a rather poor example: no one talks about XPInstall (and the majority of its surface area is now even obsolete), so .xpi is to most people completely meaningless unless they have encountered it before and know what it is. .firefox-extension would be a vast improvement over .xpi, because it says what it actually is.
Extension are only made for backward/universal compatibility file compatibility on different platform. However I do agree with the parent post, computer ought to work for us, not the other way around. Then again changing convention is harder than just type 3 letter extension.
That's an excellent suggestion. WTF does ".xpi" even mean to someone who just wants to install a browser extension?
As far as I recall, extensions became a thing with DOS. They actually had meaning to the OS, e.g. naming a file .exe would make it executable, as there was no other concept of file ownership or permissions.
In Unix/Linux systems, filename extensions have always been for the user. Before GUIs and icons, they were a convention that let the user know something about the file contents. As far as the operating system is concerned, "." is just another character in the name and extensions are meaningless. Note that most binary executables don't have an extension at all, and other files have more than one (e.g. .tar.gz)
CP/M had extensions in 1974, five years before DOS. There may be older examples, but that's the first operating system I ever used.
There was also ITS, which was one of the famous operating systems on the PDP-10. On ITS, filenames consisted of two parts, rach being 6 characters separated with a space. So you could have a file named "abc def". The second half was often used in the same way we use extensions today, but executable files were named "ts name", where name was the name of the command.
I'm not sure what format filenames had on TENEX and TOPS-10.