I think you have identified the problem. What is happening is that each site uses up a piece of the device's memory and when the on-board memory is filled with at least 8 apps and anything else it has kept it then it is so clogged up it stops functioning. The memory is like a bin being filled to the brim and needs emptying. So yes open then close each one. But now if your device has a 'data storage' section in its 'manage apps' section see if you can find a 'clear cache' section/button. 'Cache' means nothing more or less than 'storage bin' it is just fancy IT jargon. Then click on 'delete the cache' or in plain English 'empty the bin'. Or download a 'clear cache' free app from Google or Apple and just do it all the time ie 'Clear cache' or empty the bin. This should work for you.