Unfortunately, the information above isn't really helpful in performing a diagnosis. The crash you're seeing is in the Firefox process that's hosting the Flash Player plug-in. It doesn't really do much but relay messages, so it should just work. The libraries are super simple, standard libraries that would not be slow under normal circumstances. What I can tell, is that things aren't working like they should.
Given the degree to which you're currently exposed to malware infections by virtue of being on WinXP SP2 (which pre-dates all modern memory-based malware defenses), I wouldn't be surprised if you were seeing side effects from an infection; however, it's hard to make that kind of diagnosis from where I'm sitting. As we're not seeing a flood of similar reports (we're on 98% of computers browsing the web), there's definitely something pretty unique about your system that leads to this issue.
This probably isn't going to be the answer you're looking for, but I'd highly recommend taking this opportunity to move away from WinXP. Windows 7 provides a set of reasonable memory protections, and is really the minimum Windows version you should be on given the threat landscape in 2014. Windows 8 and higher provide more modern defenses, but I understand that moving to the newest thing isn't always attractive. WinXP is very, very broken from a security perspective and has reached it's end of life. We're really not testing it, and are only going to fix critical security issues at this point.
If you haven't already, you could reboot and see if the browser starts working more normally again, but you're really a sitting duck on this configuration.