Comp woes

My computer has been acting up lately. Nothing major, but it's odd and disconcerting. Every once in a while, maybe once a day, Firefox freezes up for about 30 seconds. During this time, Task Mangager can be slow to load. Just about everything else seems to work fine (although sometimes a bit slower than usual). Time passes, and Firefox resumes normal function. And then McAfee pops up a notice to tell me that Virus and Email protections have been turned off (though other services, such as the firewall, seem to be functioning normally). I click the "FIX" button, McAfee turns protection back on, and everything's fine for the rest of the day. Maybe even the next day, too.

Still, it seems suspicious.

I've done a full virus scan with McAfee. Did another one using McAfee's web-based remote scanner, just in case there was an infection that was messing with the local copy. Did full scans with Spybot, AdAware, Malwarebytes Anti-Malware, Panda Anti-Rootkit, and IObit Security 360. Everything came back clean. (I also have passive protection from SpywareBlaster and Spybot's Tea Timer.)

Ran a check-up with McAfee's "Virtual Technician" diagnostic, which turned up a missing registry key... the one that named the logfile. Fixed that, which initially seemed to help, but then the problem happened again today.

Haven't installed anything much of late. I did accidentally connect to an ad-hoc network named "Free Public WiFi" in the airport (a service the airport does provide, though with a different network name) for a few minutes, but I'm not sure I ever got a proper connection and I can't remember if that was before or after the problems started.

Thoughts/suggestions, anyone?