There is a bug in the new Firestorm 4.7.9 and Second Life 4.0.7. The bug is not much of a problem unless you play in combat games. Whirly Fizzle explains it:
Yep, it’s a bug on Firestorm 4.7.9.
I saw you already found the JIRA issue, but here it is for anyone else having the same problem:http://jira.phoenixviewer.com/browse/FIRE-19640
Workarounds for this one:
If you are wearing an attachment using llTakeControls, take it off. That’s the trigger for the bug.
It may not be viable to remove all attachments using llTakeControls though. This bug is mostly annoying combat people who use mouselook a lot & many weapons use llTakeControls in such a way that they will trigger this bug when they exit mouselook.
Switching to the LL viewer is a no go – although it doesn’t have this specific bug, it has a related bug which breaks being able to shoot pretty much all weapons in mouselook when an attachment is worn using llTakeControls or the weapon itself uses llTakeControls – BUG-11602
Best bet honestly is to roll back to 4.7.7 if this bug is annoying you too much. (Reference)
If you are playing a combat game, add your name and information to the JIRA’s.