We don't have a built-in way to do this as { and } are valid symbols that some users want and there's no standard method for adding tags like that that we could detect.
What I would recommend is making sure that the Jumi plugin is ordered before any JFBConnect plugins. That should make it so the Jumi plugin executes first and removes its tags before JFBConnect tries to generate a description for the page.
If possible I would also like to exclude the headline, marked with <h1>
</h1>
Again, we don't have a way to do this automatically. Any HTML tags should be automatically stripped, but we don't have a method to scan for specific tags and strip/keep the content within them.
Overall, the best recommendation I can give is to explicitly set the Open Graph description tag that you want to use on each page, like:
{SCOpenGraph description=My Description for the Page}
You can even use PHP within those tags to dynamically generate the description.
I hope that helps explain,
Alex