Once the url was resolved tab sync was again fuctional in SM. The next task was to get the 'Tabs from other computers' menu displayed with a proper overlay and have the about: weave-tabs page correctly display the list of tabs from other computers.
I have written an experimental xpi for testing weave tabs sync on SM. I just tested this on the new Seamonkey 2.1 Alpha 1 which has just been released (http://www.seamonkey-project.org/releases/seamonkey2.1a1/). The xpi can be downloaded from here https://sourceforge.net/projects/tabs-for-sm-wv/files/.
This xpi has tabs sync working for SM. Next step is to report a bug in BMO and submit my patch to it. I still have one issue left to resolve though. It appears the code only syncs tabs between different SM instances. FX tabs for example do not show up on SM. This needs fixing.
It seems the biggest issue in getting weave sync to work on SM is that every time weave code is changed it is written specifically for FX so there is a chance SM fucntionality will be affected.