Opera to the rescue

Opera browser support

Even though Seamonkey 2.23 is working (it is after all a ppc platform version) it is very slow, so I've been looking for another alternative and found iCab, Omniweb, and haven't found satisfaction - then I found Opera - now, the trick is the main link for the download will bring you to the latest version of Opera that will not be supported on 10.5 - but through this link at http://arc.opera.com/pub/opera/ you will be able to install Opera 12.16 the last version available supporting 10.5

http://arc.opera.com/pub/opera/mac/1216/

The one to select is the highlighted one for Intel.

Customization

Contrary to Seamonkey - Opera is pretty nice out of the box, the only thing to change is in tools/advanced/plugins

Once again disable everything - but keep Flash.