I have a laptop that has some power issues. On occasion, it freezes and I have to hold the power button for 6 seconds to get it to shut off. If I have Firefox open when this happens, it has at least happened a dozen times that I have lost all of my bookmarks, and upon launching, it will not open in a full window and the search toolbar is empty.
To me, similar to my issue, it sounds like your Firefox profile is corrupt. I am not sure how this relates to the update. However, I would uninstall Firefox, see if you can salvage your bookmarks first, than delete your profile directory. Reboot. Download/install Firefox again, and see if this resolves your issue.
Here's a How-to guide on how to back up your BookMarks - http://www.bleepingcomputer.com/forums/t/65275/savingrestoring-firefox-bookmarks-for-a-reinstall/
If you follow the guide, it will allow you to back up your bookmarks.-If they are still intact. Most of the time with my issue they were lost, so I started manually backing mine up on occasion.
Also in the guide, you will see where the Profile is located - C:\ Documents and Settings \ "your user name" \ Application Data \ Mozilla \ Firefox \ Profiles \ default.random characters \
I normally delete everything under - C:\ Documents and Settings \ "your user name" \ Application Data \ Mozilla \Also, I have never done this, but I found this when researching your issue.
It may be an easier method that you could try first: (Create a new Profile) http://www.mozilla.org/support/firefox/profile
I hope that helps.