Recover when cookies are disabled in Firefox and accessing localStorage throws

Summary:
Ref T13216. See PHI985. If you disable cookies in Firefox, accessing window.localStorage throws an exception. Currently, this pretty much kills all scripts on the page.

Instead, catch and ignore this, as though window.localStorage was not defined.

Test Plan:

• Set Firefox to "no cookies".
• Loaded any page while logged out.
• Before: JS fatal early in the stack.
• After: page loads and JS works.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13216

Differential Revision: https://secure.phabricator.com/D19832