There should in theory be a way to restart the browser without causing any security concerns, however the developers probably don't view the feature as a priority. On the official site it is seen not as a bug, but as a feature request:
People want to:
Start Tor Browser Bundle, close Tor Browser for various reasons, leave Tor and/or Vidalia running for various reasons, and restart Tor Browser later.
Again, the official line is that the developers are 'working on a way to make this possible on all platforms'.
None of the current Linux stable or alpha versions of
tor browser bundle currently implement the restart feature. This is because they do not contain the version of
Vidalia that had the feature which allowed you to restart the browser after closing it. That version of
Vidalia is discussed in this request, although there have been requests and discussion of the feature for all platforms here and here.
In summary, the aforementioned official sources make it clear that this seemingly simple browser restart feature is not so simple to implement. It would require a specific patched version of
Vidalia, a specially patched version of
Firefox (beyond the one already included in the bundle), and much work to make sure that there were no security holes introduced into the software.
There doesn't seem to be a quick way to implement a shell-script to do it unfortunately, so it's just a case of waiting for the developers to implement the feature or trying to help out with the development oneself.