Why does Safari v5.1.9 slow down?

Question

I recently switched from Firefox to Safari v5.1.9 because I found Firefox too slow.  Now it seems that Safari slows down a lot over time.  Scrolling becomes jerky and sometimes pauses.  Pages don't load/pause and I have to stop loading and restart loading.  I have a white Macbook circa 2008 with Snow Leopard v10.6.8 installed with all available updates installed.  I am running the current version of Safari v5.9.1 for Snow Leopard.  If I quit Safari and restart it, the software goes back to normal speed.  I often have 11+ tabs open and almost never shut down and restart my machine.  Any ideas?  Thanks.

Answer 1

Thanks for your response.  This morning I did some experimenting.  I ran the Activity Monitor and checked memory usage when Safari had run since yesterday, then I quit Safari and checked, and finally I restarted Safari and checked a 3rd time.  Below is a chart I made of the memory usage where the first number is prior Safari, the second number is without Safari, and the third number is after rerunning Safari.  BTW:  I have 4 GB RAM installed and have 12 tabs open in Safari.  Oh, and when I restarted Safari, 5 of the 12 tabs would not reload.  I had to close the tabs, open new ones and go back to the web sites manually.
Application - Prior Memory Usage - After Restart of Safari
Safari Web Content 1.10 GB - 441.9 MB
Safari 236.8 MB - with 12 tabs open - 230.8 MB
Flash Player (Safari Internet plug-in) 116.2 MB - 59.6 MB
Memory when computer opened from sleep - after quitting Safari - after restarting Safari
Free: 664.6 MB - 2.27 GB - 1.69 GB
Wired: 453.7 MB - 448.7 MB - 452.3 MB
Active: 2.42 GB - 847.8 MB - 1.53 GB
Inactive: 498.0 MB - 471.5 MB - 337.1 MB
Used: 3.35 GB - 1.73 GB - 2.31 GB
I seems pretty clear to me that Safari uses an extraordinary amount of memory over time and it keeps taking more causing Safari to slow down.  This is what a memory leak looks like.  It's hard to believe that Safari is so buggy when it has been revised so many times.
Thanks again for your idea.  I guess the only solution is to periodically quit Safari and restart it.  I think I will check Firefox memory usage later today to see if I should switch back.