linux firefox slow with poor threading

I have been using Firefox and Mozilla along with Opera for quite some time
on Suse 9.1 linux.
All the Mozilla derived browsers have the same problem they are terribly
slow and the multithreading is poor.
When a tab is loading nothing happens until that tab has completed
loading. Also I keep seeing files of around 470 kb loading called
"downloading control".  I haven't a clue what these files are. Opera loads
much faster and has little problem with the multithreading. I would love
to use Firefox or Mozilla but both are frustratingly difficult to work
with. I have the latest versions of all of the browsers. Incidently
Konqueror from KDE also runs much faster than Firefox.

Any ideas?