I am a longtime LastPass and Xmarks user, since both were emerging, independent and fledgling add-ons. While I like both very much, it looks like LastPass/Xmarks is lagging behind -- far behind -- other add-on developers. Here is the latest frustration on both my Windows 10 64-bit PCs running Firefox as the default browser:
Firefox just updated to version 56, and now both LastPass and Xmarks are broken because they are "Legacy" add-ons that are incompatible with the latest Web browser technology. Since the Firefox 56 update, LastPass won't populate login windows/popups and Xmarks won't sync bookmarks/favorites.
No solution that I can find easily is offered on the LastPass/Xmarks websites, nor on the forums. There are numerous complaints on the Firefox Add-In pages about this, however no response from the developer is provided.
The only solution is to try installing the beta add-ons found in the Development Channel drop-down menu. However, while the Xmarks beta works OK, the LastPass beta won't install at all, so I am stuck with using the semi-functional, now-it-works-now-it-doesn't "current version" LastPass Legacy add-on.
So, when are you going to provide apps that work on the latest version of Firefox, or on Edge for that matter? And please don't suggest that I jump to using Chrome: I value my privacy and Chrome does not.