An anecdote about the jank and pauses: I have... many (D:) tabs open in Chrome right now, and I discovered that setting Session Buddy to show the number of tabs

An anecdote about the jank and pauses: I have... many (D:) tabs open in Chrome right now, and I discovered that setting Session Buddy to show the number of tabs in its icon causes the entire browser to pause for a fraction of a second every 1-2 seconds. Clearly this is because Session Buddy is calling the "get list of open tabs" API method, which for all I know is using a global mutex that is held for as long as it takes the browser process to get and build the tab list. Perhaps something similar is happening in Firefox. Try doing the whole nuke-profile-from-orbit thing, remove all extensions, reset all the settings, etc (after backing the profile up sufficiently to be able to put it all back). It might be some obscure option or configuration flag. Given the low number of tabs it's not likely to be that.