Hmmm I use FF4 for web development mainly, havent noticed it... May I suggest Chrome for a better/faster browsing experience
Here is the solution right up to Firefox 6.. download and install: Movable Firefox Button ADD ON... press ALT, select VIEW>TOOLBARS>BOOKMARKS TOOLBAR press ALT, select VIEW>TOOLBARS>CUSTOMISE Now press ALT, and move the firefox orange button onto the toolbar - then click close. Finally: press ALT, select VIEW>TOOLBARS> and uncheck BOOKMARKS TOOLBAR ALL GONE!