[fix bug 1066865] Ignore snippets that link to about:accounts when sync is setup.

Unless I'm reading this wrong it seems to use the delay regardless of your Firefox version. Am I missing something?

As for caching, caching until the next time they hit about:home is fine, as the check probably isn't expensive. We're caching only to avoid the delay, we can afford refreshing the cache each time they hit about:home.