I have a friend who is also running 10.6.x with Firefox (also happens with Safari) and whenever he goes to a particular audio site (I think it is audion.com) he has a similar experience.
After a bit a trouble shooting the best that could be determined is that the site was throwing, via the browser, code that was "too new" for 10.6.x, which resulted in a kernel panic. May seem strange but everything else is working OK for him.
On a Mac since 1984.
Currently: 27" iMacs, Macbook Air, macOS 10.15.x,; iPhones, iPods and iPads galore!