User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:34.0) Gecko/20100101 Firefox/34.0 Build ID: 20141120192249 Steps to reproduce: Randomly once in a while while switching from one tab to another they freeze for many seconds.(if OMTC is enabled) Actual results: Tabs hang/freeze. Here is a thread in mozillazine with many users having the same symptoms. http://forums.mozillazine.org/viewtopic.php?f=9&t=2880521 For me minimizing/maximizing firefox works to break the hang immediately, if that is not done firefox takes many seconds to switch the tabs. Is very annoying though. Expected results: There should be no noticeable delay while switching tabs. And this tab hang never happens if OMTC is switched off.