Lots of duplicate tabs - can I start again?

Hi

Although this question started off with a problem in Safari it develops into a general question - hope that's okay.

Recently I started getting lots of duplicates of tabs in Safari if I restarted my iMac, and also problems getting windows in Finder to stay at the size I set them to (they would jump back to half a screen usually). I have an iMac which I bought in October 2011 (3.1 GHz, 27") and I have the latest version of Mountain Lion (10.8.4).

I have purchased a lot of software over the iMac's life (I'm a bit of a software junkie) and I suspect I've got some corrupted files. I did a search on the Support forums and as a result created a new Admin account as a test - and it was wonderful - nice clean start with Safari and Finder behaving themselves. I almost stayed in the Test account.

My questions are:

1. Does anyone know what the problems I'm having are caused by?

2. If I can't find an answer - can I delete my Library/Preferences file completely in my original account and start again? In other words - would deleting all my plist files get me the same situation as the Test account - starting over really.

3. Could I just transfer to the Test account completely and delete the original account?

I appreciate if I started over or transferred to the new account I will have to create Preferences for all my software - but in one way this may not be a bad thing as I often learn about the software I really want to use only after I've had time to work with it - and I suspect I've been too hasty installing everything on my original account (I tend to fall for software bundles as well).