First, regarding the search issue, could the Twitter search bar be the built-in Firefox search bar? if you click the Twitter icon, do you have a drop-down list of search engines? If so, you can use the Manage Search Engines link at the bottom to remove the ones you don't want. Or just select your favorite and leave the others for possible future use.

Second, regarding the Back button, some sites forward you from one page to another, creating a loop that you can't break. If you right-click the Back button or press and hold, you should get a list that lets you see whether that's the problem and lets you choose to go back to a different site.

Third, regarding the Bing toolbar, do you get an error message when you try to install?

I was finally able to get rid of the Twitter search bar. I clicked on the tiny down pointing triangle right after the Twitter icon and selected Bing.

I'm still not sure if it corrected the problem with my back and forward arrows. Before, I could click on them at times and get a " Waiting for "whoever'" and a blank screen or the same page I was looking at before. I could click several times and it would finally work. I could usually click on my Home icon and it would work, but EVERYTHING was very uncertain. I am still experiment to see how often it still happens, but I stopped using Microsoft IE because of a similar problem. When I first installed Firefox, it was fine, but I was trying to work on cookie retention or rejection and I believe that is when it got screwed up.