Start Firefox in Safe Mode
While you are in safe mode; Firefox Options > Advanced > General.
Look for and turn off Use Hardware Acceleration.
Poke around safe web sites and see if there is still a problem. Then restart.

But I insist that the thing is same in the no-addon mode. By no-adon mode, I meant safe mode. I also explicitly stated that it happened on multiple instalations independent of each other.

Because I seem to be only one to have the problem I don't suppose getting much help from anyone. That said, is there a way to debug it myself? Any verbose mode? A way to know what is firefox doing that 10 seconds?

And I'm especially curious about Firefoxe's tendenci to throw laggy tabs into new windows.

You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox profile folder that store session data.

Rename (or delete) the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox profile folder.

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Multiple_profile_files_created

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost and you will have to recreate them (make a note or bookmark them if possible).

Not the first time I read this recomendation. I'm not sure how is the sessionrestore related to tabs when browser is running (is it being overwriten every time I switch tab?) but it didn't help.

I've been now paying more attention to the issue, and I still see no system in the lagging tabs. It seems very random - though tabs that are harder to render are very likely to do this. But often, openning new tab also causes lag.

Firefox may update the sessionstore.js file to set which tab is currently active (selected), so switching tab could cause Firefox to update the file. This can also be a problem with the places.sqlite file and a large history.

You can check the number of history items in the History Manager (Library) by entering a common character like a colon in the search field (use Ctrl+A to select all items and see the total count).

You can check the number of history items in the History Manager I can't - browser will lag.

My history is very long - I don't like deleting it, because I often search old things in it. That's what history is for, isn't it?

I have already been querying how to delete useless items from history. I have already dealed with google - deleting it page by page.

I just noticed that the lag is considerable when switching out of Facebook tab.

My question now is, can I make sure no events are triggered when I switch out of tab?

LAST RESORT ! ! Reset Firefox {web link}

nothing works

Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

A reset preserves the history, so if this is caused by keeping a large history (especially for the Facebook site) then your only option would be to reduce this history and possibly move some items to a bookmarks folder or otherwise save them.

You can at least test if it works in a new profile without the places.sqlite file and see if it comes back if you copy the places.sqlite file to that profile.