GPL Firefox environmental control
4 Firefox extensions worth checking out | Opensource.com says:
uMatrix allows you to set blocking rules for certain requests on a webpage, which can be toggled by clicking on the add-on’s popup (seen in the screenshot above). These requests are distinguished by the categories of scripts, requests made by scripts, cookies, CSS rules, images, media content, frames, and anything else labeled as “other” by uMatrix. You can set up global rules to, for instance, allow all requests by default and add only particular ones to the blacklist (the more convenient approach), or block everything by default and whitelist certain requests manually (the safer approach). If you’ve been using NoScript or RequestPolicy, you can import your whitelist rules from them, too.
In addition, uMatrix supports hosts files, which can be used to block requests from certain domains. These are not to be confused with the filter lists used by uBlock Origin, which use the same syntax as the filters set by Adblock Plus. By default, uMatrix blocks domains of servers known to distribute ads, trackers, and malware with the help of a few hosts files, and you can add more external sources if you want to.
Basically, uBlock Origin – Add-ons for Firefox on Expert mode.