@naumi
if you use libertine tweektools fron open store you can scale things up to make firefox better. Also, have a look around at all the add-ons you can try. Sush as "scroll anyware".
For Falkon, if you install plasma window manager, you will get settings to mess around with. themes and button size. However. Having that setup is messing with firefox, making things too big if you want to have booth firefox and falkon. (for example as isolated browsing)
So, a bit tricky there.