Browser goes into "Not Responding" mode when typing in any input field
OS: Windows 7 Firefox Version: Current, no extensions or add-ons active
This problem started out of the blue a month or two ago. When I type in the search box or any input field on a web page, more often than not, the browser will go into "Not Responding" mode and I have to exit and restart. At the same time this started, the same problem also started happening when a pop-up window would appear (perhaps only those with input fields?). The problem with input fields seems to happen most often when they are trying to auto-complete what I am typing, but turning this off in the search box did not end the problem there, just made it happen a little less often.
I tried doing a 'refresh' on Firefox, that had no effect.
If I run Firefox in troubleshooting mode, the problem does not occur.
I do not think this is a virus problem; I have Kaspersky running, and I haven't seen any other telltale signs.