In OS X Lion, I was very disappointed to see that they took the thumbnail resize slider out of Finder windows in the default install. Thankfully, there is a simple solution…to that initial problem.
The slider is a part of what OS X refers to as the Status Bar. To re-enable the status bar, all you need to do is open a Finder window and choose View > Show Status Bar.
Once that’s done, your status bar (along with the thumbnail resize slider) will re-appear.
This setting should be retained whenever you re-open a Finder window.
…But It’s Not Working…
However, I’ve found that sometimes the slider itself just doesn’t work. I can drag the slider back and forth, but the icons don’t change size at all. The solution to this is simple, but not permanent.
You will notice that there is a quick key to the Show Status Bar menu option ( cmd + / ). When the thumbnail slider isn’t working, just push cmd + / twice. The first time, the Status Bar will go away, and the second time it will reappear. Toggling the hide/show status bar option seems to reset the operating system’s perspective on the icons. The slider should work now.
Did this help solve your problem? Do you have a solution to making the slider work permanently? Share in the comments!