Nasrin,

Was sorry to hear that you got clobbered by Cerber3 ransom ware. Suspect you picked it up via Its usual delivery as an exploit from a linked page from email message or when following a web page link.

The NoScript plugin for Firefox is pretty good for preventing delivery of the Exploit of the malware to your computer--just checked and it seems fully accessible in NVDA

Here is the link to the project page:

https://noscript.net

There is an install button on upper left edge, can be reached via keyboard, labeled:  "Install NoScript, it's Free and Open Source" -- it is a link to a Firefox .oxt extension and will place a program button on the main toolbar next to the Home button. The default mode should function well without interfering too much with your web browsing--but you will find occassion when you need to allow "exceptions" to permit pages/content you know to be OK to run. That can become a bit annoying, but if you "allow" your usual sites and applications the annoyance goes away pretty quickly.

Unfortunately on computers already infected and with encrypted files they can not be recovered--the encryption can not be reliably reversed--and I would not trust the paying a ransom to deliver a viable decryption string. So a restore from a backup is the only safe option, in other words make and keep backups current.

For protection targeted against "ransomware" encryption there are several specific solutions--but I have not checked any of them for Accessibility with NVDA

Malwarebytes has an ongoing beta of its Anti-Ransomware project -- here:  https://forums.malwarebytes.org/topic/177751-introducing-malwarebytes-anti-ransomware-beta

HitMan Pro has its Alert active anti-Exploit product -- http://www.surfright.nl/en/products

TrendMicro's  Maximum security block encryption -- http://www.trendmicro.com/us/home/products/software/maximum-security/index.html

Good luck!

Stuart