It appears a Firefox add-on does not have a unique ID, or hard to find. Any new installs are not working because every browser has a different ID which needs to be manually added in Trello API page, which is obviously not feasible.
Task: Try to find the unique ID of the add-on, or find a way to make sure the Trello API can permit calls without the allowed-URL (unlikely)
It appears a Firefox add-on does not have a unique ID, or hard to find. Any new installs are not working because every browser has a different ID which needs to be manually added in Trello API page, which is obviously not feasible.
Task: Try to find the unique ID of the add-on, or find a way to make sure the Trello API can permit calls without the allowed-URL (unlikely)
Here is the firefox extension - but obviously it won't work - https://addons.mozilla.org/en-US/firefox/addon/eztrackr/