the first version of Xmarks supporting WebExtensions and e10s.
https://addons.mozilla.org/addon/xmarks-sync/reviews/919646/ two of five stars:
+1 for the progress but then -3 because … there’s no GUI … LastPass support ticket 6101942
The initial response from LastPass suggested that 64-bit Firefox is not yet supported.
Further investigation suggests to me that update installation failed. A repeat installation was successful, I’m now using 184.108.40.206a with Firefox 55.0.3 (64-bit) on FreeBSD-CURRENT so I’m asking LastPass what’s meant by ‘not supported’.