you are running a very old version of firefox together with outdated plugins - all sorts of issues & security threats can arise from that, so i don't know if the integrity of your system is still in place.

the first thing I'd recommend is to check the status of your plugins at https://www.mozilla.org/en-US/plugincheck. if they are outdated please upgrade them or if there's no update available for your system deactivate them in the addons manager when you don't depend on them.

then please update your main version of firefox too. unfortunately macs on the powerpc platform are no longer supported by the latest versions of firefox - 3.6.28 is the last firefox version that will work. but you can try the builds from the third party project tenfourfox, who have ported firefox so that it can run on old hardware.

Now for your problem, I would try, if updating Firefox doesn't work, running Firefox in Diagnose Firefox issues using Troubleshoot Mode. It is possible that you have an extension which is interfering with Firefox's normal operation.