I previously reported that we found a memory-related problem in the Fennec Windows Mobile pre-alpha release. Bug 477956 was the primary place to track our efforts to fix the problem. However, it became clear that porting jemalloc to WinCE was the best way to handle the situation, so bug 478044 became the bug to watch. As you can see, we are in the process of getting the fix reviewed and landed.
Using our own memory allocator gives us much more flexibility and control. We can workaround the memory management limitations found in WinCE. The next version of WinCE makes some nice changes to memory management.
A few internal test builds have been made, and with a high level of confidence, we can say that the memory problems have been solved. Once we get the fix landed, you can expect new Fennec builds for Windows Mobile.