I have XP pro, Firefox 1.9.1.3593, McAfee security center 9.15, virus scan 13.15, personal firewall 10.15, backup and restore 3.15, and parental control 11.15 (disabled.) Firefox crashed so many time that I removed it about a month after I installed it this summer. It hated tabs. It would lock up for about a minute, then shut down. This happened daily.
Might try upgrading.