And if you care about what's in it just read the release notes.
I think it is in part a difference between websites oriented to the public and websites oriented to companies, where browser versions can be more complex than a self-updating browser.
But either way, I don't think this is a particularly important issue.
Calling it Firefox 13.17.6 is not an improvement.
There is no right way to decide what is a major release. Whatever you do, some users will think a major release should have been classed as minor, and vice versa. It's ultimately easier for everyone if you don't make the distinction.
Let the latest version be called Firefox and then adjust the previous versions to Firefox -1,-2,-3,-4,-5.. -76
I have been saying this from the day this was announced, so not sure this is "eight years late" or an eight year old unresolved bug.