I have legacy plugins that need to stay enabled. I've learned you can disable checking the blocklist with extensions.blocklist.enabled, but this doesn't re-enable plugins that were previously disabled.
Is it possible to enable specific plugins in a way that can be deployed to a large organization?
as far as i know this can't be done in about:config unfortunately, since the pluginreg.dat file is the only place where the information about the status of plugins is stored. one thing you could try on a machine level is to move the location of the plugin's .dll file (maybe to the \plugins subfolder inside the firefox installation directory), then it may be re-detected and treated as new plugin which should be set to active...
I figured out you can refer to specific add-ons in preferences using extensions.<GUID>.property, but I couldn't find any documentation and it appears to only work on themes and extensions and not plugins.