A Firefox browser extension has returned and is available for Firefox 48(released 2nd Aug 2016) and up.
You can get the browser extension from https://www.bugherd.com/extensions
Due to functionality required by the BugHerd extension we're unable to list the BugHerd extension in the Firefox addon store, so you may see this warning when installing. Don't worry about it.
We're working to adapt the browser extension to be compatible with the Firefox addon store requirements so as to avoid showing this warning in future.
To ensure BugHerd appears on the correct URLs for each of your projects, review and correct the URLs on this page: http://www.bugherd.com/extension/projects