It appears as though Valve is starting to gear up for SteamOS 3.4! Our good friends over at LinuxGamingCentral noticed that SteamOS 3.4 has been sneakily pushed out.
While this doesn't seem to update much, it does update Firefox, changing it from the version baked into the OS, which was outdated, into the Flatpak version so it can be updated consistently. This was proven by going into Desktop mode and clicking on the Firefox icon. You are immediately taken to the Discover Store to install Firefox via a Flatpak.
Heads up though, doing this will reset any bookmarks, history, and other settings you have put on for your Firefox browser initially.
It is possible the update is not final, as the only way to access it is by enabling developer mode, turning on the ability to show advanced update channels, and then selecting the "Main" channel from the "Steam Deck Stable" branch. This can't be accessed in other branches, so it is still very possible it is being worked on.