Q: Problems following update

Hi,

I normally ignore the suggested updates for my new-ish iMac (owned since April 2012) but finally downloaded the updates about two weeks ago.  Now I can't use Safari.  It loads the first page but will not leave that page.  If I enter a new url, it stays on the first page and evenutally replaces the new url with the current one.  I can't open Firefox at all.  Now we use Google Chrome but it's slow, especially when I'm using my Yahoo mail.  Finally, I can no long post on my friends' blogs - I enter the information, enter my id, then everything I've typed disappears and nothing is posted.  What can I do to fix these problems?