It might be well worth a look at your 'Manage Applications' option which you can access by touching on menu whilst in the front screen - maybe you're up against a memory limit. This will tell you how much memory you have used up on apps, and give you the opportunity of shifting some of them to the sd card. Also, it might be worth clearing both data and caches from each browser.
Once you have your list of applications (make sure you have clicked on 'all' tab) you get an indicator at the bottom showing you how much spare memory you have, then click on each app to see if a) you still want it - if not uninstall it, b) if you still want it, can it be moved to sd card? and c) in the case of the browsers, it might be worth clearing their data and caches if not 'greyed out'.