Internet Browsers Constantly Fail- Safari and Firefox

About a month ago, my computer started randomly quitting out of Safari while I was viewing webpages. They weren't games, videos, anything like that, just news sites or primarily text pages. It would happen about once an hour, maybe twice an hour. After about a week, I got frustrated and installed firefox. For three weeks, I had no problems. Now, in the last four days, it has started doing this again with firefox. I tried using Safari, and had the same problem. I've run all the software updates, and nothing else seems to be having problems. Unfortunately, firefox quits much more frequently, up to 10 times in an hour, making it very hard to get anything done. Please help!