By opposition, every application on Firefox OS is based on either standard HTML5 or currently-being-standardized extensions. This means that Firefox OS apps should be cross-platforms.
Edit: see also http://news.ycombinator.com/item?id=4189634
In effect, this means that webOS has almost all the drawbacks of working with HTML5 (no static analysis, performance often difficult to predict, etc.) but none of the benefits (cross-platform, ability to use CoffeeScript or GWT or OCaml or any other language that compiles to JS).
By opposition, Firefox OS apps are cross-platform, can be developed with any tool, etc.
edit Yes, it is possible to write apps using standard HTML5 for WebOS. What is impossible is to write apps using standard HTML5 for WebOS that take any advantage of WebOS (sending SMS, receiving phone calls, etc.). By opposition to Firefox OS, in which even SMS, phone calls, etc. are based on open standards.
Now available for desktop and cross-browser development - Enyo 2.0 now runs across mobile environments and desktop browsers including Chrome, Firefox, and Internet Explorer
IIRC, WebOS also had APIs for, say, sending or receiving SMS, vibrating the device, etc – and none of these were (or are) standardized.
That is incorrect. Apps written for webOS that use the EnyoJS framework are currently seen running on iOS, RIM (Playbook), Android, and even in the Chrome web browser.
In other words, while EnyoJS may be cross-platform, it represents only a small fraction of the features of WebOS.
I mean, if they are unique to devices for which they make sense (i.e. phones) than webOS' APIs seem to be just as standard.
What I was pointing out is that EnyoJS or WebOS or Tizen (afaik) do not make any effort at such portability. Sending a SMS makes as much sense on a WebOS-based device as on an iPhone, an Android smartphone or any other platform. This is one of the key differences between initiatives such as WebOS, Windows 8 or, to a lesser extent, Chrome OS on one side and Firefox OS on the other side. While these OSes offer the features of HTML 5 and some proprietary, non-standardized, non-portable extensions APIs for taking advantage of platform-specific capabilities, Firefox + Firefox OS push to make these capabilities 1/ accessible on all platforms where they makes sense; 2/ standardized so that other browser or os vendors can implement them as they see fit.
The difference is subtle but meaningful. This is the difference between "come and program for my silo platform" and "come and program on everybody's web platform".