This is precisely the kind of task that Policies for Firefox for Enterprise were created for. You may lock extensions based on their ID. If you are not sure where to find the extension ID, look inside the xpi file, the manifest.json
contains the ID as well.
Add that ID to a suitable policy, for Firefox 66.0 (or 60.6 ESR) on Linux that would look like this:
$ cat /usr/lib/firefox-esr/distribution/policies.json
{ "policies": { "Extensions": { "Locked": ["https-everywhere@eff.org"] } } }
Note that json files are just one way of configuring such policies, e.g. they are fully integrated into Windows AD or Local Group Policy, using those is likely preferable on applicable platforms.
Consider switching to Extended Support Releases (ESR). Firefox changes at such a rapid pace, most configurations you apply to mainline releases are often going to cause issues after just a few months.