''[Locked as a duplicate of https://support.mozilla.org/en-US/questions/1258024. Please follow up there, thanks.]'' After several weeks of Adblock giving me start-up messages, the app has disappeared from my machine. When I got the site to download it (https://addons.mozilla.org/en-US/firefox/addon/adblock-for-firefox/), the download fails and I'm told to check my connections which are fine. This happens with all adblockers I've tried on the site. I haven't added any security software. I have Firefox 66.0.3 with Windows 7.