I used to have a JIRA to Omnifocus Script which fell into disrepair for a bit.
It worked well, but as the Mac modernized itself it ended up with a lot of issues.
So I rewrote it by splitting it into a front-end (JIRA) and back-ends (the different task managers) for Yosemite and El Capitan. Now it’s called JIRA To Task Managers.
The one I use and support is JIRA and Things, which is the task manager I’ve been using lately.
Take a look and have fun!