Hi slomire, a coin mining script could come either from: * an add-on * a web page you visit Let's check your add-ons first: You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either: * Ctrl+Shift+a (Mac: Command+Shift+a) * "3-bar" menu button (or Tools menu) > Add-ons * type or paste '''about:addons''' in the address bar and press Enter/Return In the left column of the Add-ons page, click Extensions. Then cast a critical eye over the list on the right side. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? Anything you could live without for 12 hours? If in doubt, disable (or remove). Any improvement? For websites, if you do not already use a content blocking extension, you could consider one such as the following: https://addons.mozilla.org/firefox/addon/ublock-origin/ It has lists of ad servers AND coin mining sites. As with any content blocking add-on or feature, some sites will be broken without the blocked content. You will need to be comfortable making exceptions from time to time on trusted sites.