All of your extensions or only some of them? Are you able to use the Enable button on the Add-ons page to re-enable them? Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Note: Disabled extensions cluster at the bottom.

If ALL extensions are disabled and NONE can be enabled, you might be starting Firefox in its Safe Mode. Does that sound familiar?

All of them are appearing disabled. I re-enable them each visit on the browser.

Start your Computer in safe mode with networking. Then start Firefox. Try Safe web sites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Normally it is suggested to start Firefox in Safe Mode and not the computer.

Do you use any utility/security software like Advanced SystemCare that may revert browser settings changes between Firefox sessions? Sometimes this is called browser protection, or home page protection. If so, try disabling that feature, at least until you have Firefox working correctly.

James said

Normally it is suggested to start Firefox in Safe Mode and not the computer.

unless the problem is an outside program.

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

Delete the extensions.* files (e.g. extensions.json, extensions.sqlite, extensions.ini) 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 or not compatible extensions in "Firefox/Tools > Add-ons > Extensions" then click the Tools button at the left end of the Search bar to check if there is a compatibility update available.

If this hasn't helped then also delete possible addons.json and addons.sqlite files.

You can check for problems with preferences.

Delete possible user.js and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in the current Firefox release.

• http://kb.mozillazine.org/Preferences_not_saved
• http://kb.mozillazine.org/Resetting_preferences

Thanks for everyone.