What was the technical limitation because the Firefox ports didn't went from version 10 to 11 and follow on?
Short story, by FF10 I was the only one left building and halfway through 11 it broke and I didn't have the skills to fix it.
Long story, after FF4 they dropped support for non-ipc (interprocess-communication allowing tabs to run in their own process so when Flash crashes it would only take out the tab it was running in, Flash crashing is a problem on all platforms) and mostly Walter kept the ipc patch alive. This was a very tedious process as the patch grew to 280KBs (980+ lines) + supporting patches of about 75kb which had large amounts that needed to be applied by hand. Walter did an excellent job of keeping the patches up to date but had personal problems and got tired of rebasing the patches and moved on.
The other problem was development moved on under the assumption of IPC existing so more things didn't work. I had to remove various things like battery status that were aimed at mobile devices anyways. Eventually most of the HTTP code was rewritten in such a way that I didn't have the skills to fix it.
Also I go through phases of working on it, then getting sick of hours of typing #ifdef MOZ_IPC #endif, then trying to figure out the remaining unresolved symbols.
At this point I feel that without IPC support which Rich estimated at a man-month of work for a skilled developer we won't go on. It is being worked on though not by me.