Safari browser overlapping lines

Hello,

I hope that you can help me with this. I am using Safari 4 Beta and I also use Firefox for browsing. However, I have no problem with Firefox but sometimes pages do not display properly on Safari, I mean lines overlap each other up or down or sometimes the end of one line overlaps the beginning of the adjacent line. I have tried to look into Safari preference to check out formatting spaces but could not find the answer. I would appreciated your input. Thank you very much.

Mac OS X version 10.5.6
processor 2.4 GHz intel core 2 Duo
Memory 4 GB 1067 MHz DDR2