Waterstones isn't strictly a plural, it's produced from what was originally a genitive; they changed their name from Waterstone's in 2012 by simply removing the apostrophe because they thought it looked better.
Since Halfords was named after a street named Halford Street, one could argue the same thing happened here.
Many company names that end in s were also genitive, but never using the apostrophe (of the various companies and chains set up around the world by Frank Winfield Woolworth and later inheritors, some where called Woolworth, some Woolworth's and some Woolworths, with the latter two just being stylistic choices).
Not that it really matters. People will likely think it came from "Norton's", but whatever it came from it will now be one name that is a proper noun referring to a single company. There are no grammatical issues here, just stylistic decisions. (And legal issues; set up in a line where an existing company has built a brand around the name "Norton", and you can expect them to sue you).