Unfortunately, I am unable to open your attached screenshot. If possible, can you please try uploading your screenshot again?

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
• Anti-Rootkit Utility - TDSSKiller
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• 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. Windows 8 has antivirus built-in already.

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

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

There was a problem with the "Get Add-ons" section of the Add-ons page the other day. Maybe it's still that? Try installing from the Add-ons site instead:

https://addons.mozilla.org/firefox/

I went to add ons website and then tried to install one and there was a message that adding of extensions had been disabled and do i want to enable it. I enabled it and the option was available again in the addons tab. Though i don't know why it got disabled by itself in the first place.

I didn't even realize it was an option to completely disable installation of extensions. Glad you found that!

You can inspect and manage permissions for the domain in the currently selected tab via these steps:

• Click the "Site Identity Button" (globe/padlock) on the location/address bar
• Click "More Information" to open "Tools > Page Info" with the Security tab selected

Go to the Permissions tab (Tools > Page Info > Permissions) to check the "Install Add-ons" permissions for the domain in the currently selected tab.