Editing multiple declarations isn't easy. You need to double-click, enter the property/value, confirm, double-click the next one and so on. Using tab to valid the actual declaration and go to the next one could help.
Bonus: This will also help adding new declarations at the end of the rule.
*** Bug 27673 has been marked as a duplicate of this bug. ***
I can't seem to mark this as a duplicate of bug 27673, which has patches for this behavior.
This can be marked as Resolved / Fixed, but I don't seem to have the privileges to do that!
I just gave you permissions to do it. Try it next time.