LastPass v4.9.0+ (including 4.9.1.1) fail to work for Waterfox, Firefox ESR, Cyberfox, Pale Moon and other Firefox forks, with no menu showing when click toolbar button, though it shows up for Firefox Nightly. Note that the Universal Installer is sometimes behind a version, as it only installs 4.7.1 (not 4.9, thankfully in my case). However, you may want to set Update to Off in Addon Manager for LastPass to prevent upgrading back to 4.9 if it doesn't work for your browser, after downgrading.
Tip: If you want Copy Password, then either A) run the Firefox Universal Installer (https://lastpass.com/misc_download2.php) (works even for Waterfox) or switch extension to 2.0 mode (using this page: https://lastpass.com/change_ver.php - not sure if 3.0 mode does too, or more likely is just to be used to revert back to 4.0 mode), or install 3.x version of extension.