Mac stalls, esp when starting firefox

For the past several weeks - I think possibly since the last update of firefox - the browser stalls the first time I run it after turning on the computer. I should perhaps not use the word "stalls" because it usually gets there, but the spinning wheel takes quite a bit of time. After the first opening of the day it operates normally.

Possibly related - I just got a message that I need to upgrade several applications so I said go ahead and the upgrade box sat there stalling, really stalling, and everything else slowed while it was trying to decide whether to upgrade or not, I guess, until I just shut down the computer.

I'm running 10.5.6 - I should update my profile.

My computer is overloaded with files but not as overloaded as it has been in the past, when it actually ran better.

Any ideas why it would slow like this?