Firefox uses a filter that doesn't give false positives [1]. If your site is blocked (even intermittently) there, it is in Google's malware list. [1] Actually,

Firefox uses a filter that doesn't give false positives [1]. If your site is blocked (even intermittently) there, it is in Google's malware list. [1] Actually, the odds are 1 in 2^128 if Google's servers are up, and 2^32 if Google's servers are down.