You can always manually right-click on the bookmark and choose Reload Live Bookmark, but that’s hardly efficient if you have dozens of feeds bookmarked.
You can change the default interval for all live bookmarks with a config setting. Just type about:config into the address bar, and then filter by the following key:
If it doesn’t exist, which is most likely the case, then right-click in the blank area and choose New \ Integer.
Copy in the key from above as the name, and then set the default value to 1800, which is 30 minutes in seconds.
The default value used internally is 3600 if the setting does not exist. You should be careful about not setting this value too low, as you might get banned by the server you are trying to connect to if you have the browser updating too often. The minimum value accepted is 60 seconds, but you should never set it that low.
