You’re correct, the other commenter missed the “2 computers” part of your comment.
You can run multiple Steam games at the same time on the same PC, but not on different PCs.
That is, unless you take advantage of Steam’s “offline” mode. If you launch Steam in offline mode on the secondary computer, you’ll be able to play already-downloaded Steam games on that PC, while still being free to play Steam games normally on the primary computer.
Mozilla’s not going to undermine the thing that’s going to drive the largest adoption of Firefox in years.