Very unpredictable add-on. When it works it is a major productivity boost. It has always worked fine on my old Windows 7 desktop but on my Windows 10 laptop, after several recent major version updates to Firefox this add-on fails to log me in to my LastPass vault, with no useful diagnostic messages. This occurs before and after I uninstall and re-install the add-on, which is the only one I am running. Forum advice seems to be to re-create my Firefox profile, which is overkill for this problem. When the add-in was logging me in, the behaviour on some sites was inconsistent and unpredictable, in terms of whether the Add-In was displayed, what options were displayed, whether the in-field options to fill were present. I assume this is a consequence of the evolution of web technologies. Given the rapidly increasing costs of LastPass then this needs to be addressed.