More sleep, less work.

Nah, that still happens on latest nightlies when Firefox’ uptime reaches 12-14 hours. Restarting the browser helps.

@Drugoy Unless you had an hang issue solved by my previous suggestion (thus through the Places Maintenance Addon), you are likely seeing a different issue. The issue I worked on would not cause a worse experience along the same session, but after many sessions or after a large history import/sync.
This is not intended to fix any hang issue one may hit (for example lately I’m having some hang issue related to focus events and Flash 11), just a specific one.

Yes, maybe I’m seeing a different issue.
But it still hangs for me when browser’s uptime reaches a few hours (it appeared that it’s not 12-14 hours, but even less): the whole browser freezes for a few seconds once every 20 sec.
I wish there was some kind of a diagnostic tool, something like CPU consumption log of different threads inside the firefox process.
As I think it may be some particular extension causing this, but to find out which one – I have to go through a long and painful procedure of creating a new profile and multi-step (by parts) migration from the old profile, as I’d like to save all my data (all the extensions, all the setting for them, all the history, all the passwords, all the prefs, etc).

Drugoy, I recently found a situation where “undo” data in the session was causing hangs like you describe. how big is your sessionstore.js file?

sessionstore.js111kb
sessionstore-1.js 392kb

Some other guys from my local forum – they all experience the same hangs.
It also appeared, that we all use x64bit version of Nightly.