I have the same problem, it's not occurring all the time, but very often. Slow response in scrolling websites, switching between tabs and very laggy when scrolling pdf documents, comparing to chrome. There's a feeling like firefox just hangs up. Can't be the computers fault, because other software works with no problems while firefox isn’t responding. w7 Professional, i7, 4gb ram, no problems with chrome, ie. Enabled plugins: Adobe Acrobat 10.1.1.33 Shockwave Flash 11.0.1.152 Silverlight Plug-In 4.0.60831.0 ( Just disabled it )