I tried WebRunner (former Prism, they have the same AppCreator GUI), please read my previous review March 13, 2011.
It has a strong memory leak: after 12h on the same site it can reach to 122MB, it takes 2 - 3 times more memory than Prism... but have some interesting features and better look.
I have a triple FF installation (with Prism 1.0b2), so when I install an Add-On it goes to all 3 FFs. The results:
1. FF3.5 (my Prism App Creator platform): WebRunner is incompatible to FF3.5, I did not try to cheat the Compatibility Check, so WebRunner is inactive in Extensions window... IS THAT RIGHT? When I clicked "Create WebRunner Application" in menu, the AppCreator GUI shows up!!!... but not worked. By the way the Prism stopped to work too;
2. FF3.6 (my Safe Surf platform): I installed WebRunner here but it did NOT work, probably due to some add-ons, maybe Prism 1.0b2..., that stopped to work here too;
3. FF4RC (my Testing platform): WebRunner WORKED fine. Prism is not compatible to FF4 (inactive).
That is the solution for the Prism addicts and FF4: FF4RC + WebRunner v4.0b12, if you don't mind to waste some memory.
For myself I uninstalled the WebRunner and I kept my old and stable platform: FF3.5 + Prism 1.0b2 (see my previous review).