User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:33.0) Gecko/20100101 Firefox/33.0 Build ID: 20141011015303 Steps to reproduce: Happens rarely when switching tabs. It happens at random since Firefox 33. I do not have any steps to reproduce this bug as it happens randomly every few hours. Some other people reported a similar bug here: http://forums.mozillazine.org/viewtopic.php?f=9&t=2880521 Actual results: Firefox hangs(page does not switch, hover effects remain frozen) for about 10 seconds before switching the tab. The rest of the navigation ui remains responsive. In fact the tab would switch instantly if the window was minimized or the 'Open Menu' button was clicked. Actions seems to be queued or have taken place but not displayed while hanged. Expected results: Instant tab switching.

I dupe with bug 1065463, they have the same underlying issue, freezing during tab browsing.

I have the same freezes sometimes with removing or switching tab. It started with version 33.0 and continues now with 34.0. Win 7 sp1 x64 fully patched. NVidia NVS 4200m version 341.05 (latest driver as of this posting). When it happens while switching, the header for the tab switching to paints/draws fine (it's now the current tab), but the page content from the previous tab is still displayed (only the header switched). It's very annoying.