This may be your problem, All Firefox v52+ Releases disables all plugins including Flash [https://support.mozilla.org/en-US/kb/npapi-plugins Why do Java, Silverlight, Adobe Acrobat and other plugins no longer work?] {web link}

''<p>Sam99 [[#question-1343148|said]]</p>'' <blockquote>want to use Lusha plugin, but Firefox deemed it as unstable, but I want it anyway, how do it use the extension ? </blockquote> Lusha doesn't seem to know whether to call their product "plugin" or "extension".<BR> The extension can't be found on the official Mozilla add-ons page; &nbsp; it has been removed for the reasons that you mentioned. There is however an alternative that you might like to try:<BR> https://addons.mozilla.org/en-US/firefox/addon/email-extractor-aeroleads/?utm_source=addons.mozilla.org&utm_medium=referral&utm_content=search And maybe you'd like to take a look at this extension:<BR> https://addons.mozilla.org/en-US/firefox/addon/signalhire-best-contact-finder/?utm_source=addons.mozilla.org&utm_medium=referral&utm_content=search

See also: *[https://bugzilla.mozilla.org/show_bug.cgi?id=1617192 1617192] - Extension block request: Lusha (<i>please do not comment in bug reports<br>https://bugzilla.mozilla.org/page.cgi?id=etiquette.html</i>)