I don't have that problem with the non-portable Firefox. And I don't remember it happening when I first got Portable. Maybe it was a different version then. But now...sheesh.
I'll start to type a password and after three letters nothing shows up. I wait about 5-10 seconds and I can type again. Or I pull down a menu and wait...until it lets up and drops the menu. I can't even click anything during the hangs. The buttons won't highlight as the mouse goes over.
It started out being just an occasional hang but now it's really frequent. And annoying. I was trying to get out of the office one day. I just wanted to see if my post to a group had posted before I left. All I had to do was refresh the page, scroll down, and then scroll back up to log out. It hung after each little step. I refreshed. Then I had to wait to scroll. Then I had to wait to scroll back up. I had to wait before I could hit the link to sign off. Then I had to wait to hit the X to close the program.