It is possible that there is a problem with the file(s) that store the extensions registry.

Delete the files extensions.* (e.g. extensions.sqlite, extensions.ini, extensions.cache) and compatibility.ini in the Firefox profile folder to reset the extensions registry.

• https://support.mozilla.org/kb/Profiles

New files will be created when required.

See "Corrupt extension files":

• http://kb.mozillazine.org/Unable_to_install_themes_or_extensions
• https://support.mozilla.org/kb/Unable+to+install+add-ons

If you see disabled, not compatible, extensions in "Tools > Add-ons > Extensions" then click the Tools button at the left side of the Search Bar (or click the "Find Updates" button in older Firefox versions) to check if there is a compatibility update available.

If this hasn't helped then also try to delete the addons.sqlite file.

This does not helps. Addon manager don't work at all. I've also found another error message just after firefox starts:

Метка времени: 21.02.2013 11:01:56 Ошибка: [Exception... "Component returned failure code: 0x8000ffff (NS_ERROR_UNEXPECTED) [nsIPrefBranch.setIntPref]" nsresult: "0x8000ffff (NS_ERROR_UNEXPECTED)" location: "JS frame :: resource://gre/modules/AddonManager.jsm :: AMI_startup :: line 469" data: no] Источник: resource://gre/modules/AddonManager.jsm Строка: 469

The same problem in Safe Mode

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

I've done something like this, I've packed all mozilla files, from all locations, then reinstalled it, and copied some files from old profile.

The browser looks even better than with ald profile, even after upgrade. It is a bit surprize for me that it can not make correct upgrades from 15 to 19 version. Anway, solved.