Browser extensions can perform a number of tasks like access filesystems, gain telemetry on what processes are running on a host, view browsing history, etc. Here is a list of the APIs that Firefox makes available to Extension developers https://github.com/krypted/extensionsmanager/blob/main/Firefox%20Extensions/apisaslist.

Firefox for Mac stores a list of extensions in /Users//Library/Application\ Support/Firefox/Profiles//extensions.json (the first * denotes there's a manifest for each user and the second * denotes there are multiple profiles with their own sets of extensions for each Firefox user within that Mac user account). To see a list of all of the extensions in Firefox, the following find command can parse through the directory (or directories), read the extensions.json, and find the name field.

cat /Users/*/Library/Application\ Support/Firefox/Profiles/*/extensions.json | sed 's/"name"/\n"name"/g' | grep '"name"' | awk -F',' '{print $2}'