Following a loss of many tabs I sent to another Firefox session from my iPhone using the Firefox Send Tab to function (long story...), I noticed that no log of these tabs was kept. Recovering these tabs thus proved to be impossible due to the way Sync works.
This is why I propose to keep a log of all tabs sent using Firefox Sync, two options seem prudent:
a) the log file is shared as some sort of common history and can be accessed through Sync, even from other devices
b) the log file is just available on each device and tabs can only be recovered on that device only to then be potentially resend