Z 5 z 5 hwěžkow pohódnoćeny

wot zorglubz dnja Jan. 19, 2010 · trajny wotkaz

So the bug persists, through the versions up to 3...
Open the XPI file as a ZIP file,
edit the install.rdf :
change :
1.6
to
4
for instance,
update the install.rdf and install the
sync_on_arrival-1.3-mz+tb.xpi

You're good to go and it's still working.
I wish one day this extension will be useless...