Browser freezing might not be related to WiFi at all.
What other apps do you have running recently?
When you exit apps do you use the 'Back' button in the Apps and exit (which closes the app) or do you just press the 'n' button (which just keeps the app running in the background)?
What happens if you go to the shop and download one of the other browsers like Puffin or Dolphin or Maxthon? Do you get the same issue?