Please check if all your plugins are up-to-date. To do this, go to the Mozilla Plugin Check site.

Once you're there, the site will check if all your plugins have the latest versions. If you see plugins in the list that have a yellow Update button or a red Update now button, please update these immediately.

To do so, please click each red or yellow button. Then you should see a site that allows you to download the latest version. Double-click the downloaded file to start the installation and follow the steps mentioned in the installation procedure.

Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

Thanks for the support. I have followed your suggestion but all my plugins are up to date.

In a safe mode my keyboard was completely disabled. Neither letters nor numeric keypad were responding.

I must admit that I am not an expert in computers. I am not always sure if I did everything as suggested but this time after rebooting the system in safe mode it was not possible to type anything (I tried in Firefox but also in Calculator and Word)...

Anyway, thank you for suggestion.

Still looking for a solution...

Do a malware check with some malware scanning programs on the Windows computer.
Please scan with all programs because each program detects different malware.

Make sure that you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender: Home Page:
  http://www.microsoft.com/windows/products/winfamily/defender/default.mspx
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• Anti-rootkit utility TDSSKiller:
  http://support.kaspersky.com/5350?el=88446

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

Cor-el, thank you for detailed instruction.

I have done that with Avast but it seems that I should try with other suggested software. Only it will take some time and I cannot do that now. I shall try this evening and will report about the outcome.

Problem still exist - looking for a solution. You may see how this appears on the screen at the attached picture.

That looks like a JavaScript pop-up, so it may be created by JavaScript that runs on this web page that is meant to prevent you from using some specific navigation keys while being on this page.

It is possible that this script isn't working properly in the current Firefox version if it blocks all keys.

Reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

Clear the cache and the cookies from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"

I am still looking for a solution of my problem but just ffew minutes ago I received following information from the Eurobank which I think might be of interest for other users of Firefox.

Quote: Postovani, Ovim putem zelimo da Vam skrenemo paznju da je kompanija Mozilla, bez prethodne najave, u najnovijoj verziji svog pretrazivaca onemogucila pristup svojim sertifikatima za sve Java aplikacije. Ukoliko ste sertifikat izdali koristeci Firefox i dobijate poruku "Sertifikat nije pronadjen" potrebno je da sertifikat izdate koristeci Internet Explorer. Nakon uspesnog izdavanja sertifikat cete moci da koristite i na Firefox pretrazivacu. Trenutna stabilna verzija java aplikacije koja je preporucena od strane Banke jeste Java 7 Update 21. Po izlasku nove verzije Java aplikacije molimo Vas da ne radite update dok se ne utvrdi kompatibilnost sa eBanking aplikacijom o cemu cete biti obavesteni naknadno. Srdacno, Vas Eurobank eBanking tim Unquote

With this memo we want to draw your attention that company Mozilla, without prior notice, in their latest version of their browser has prevented access to their certificates for all Java application. If your certificate was issued using Firefox and if you receive message: “Certificate not found” it is necessary to issue the certificate using Explorer. After successful issuance of the certificate you will be able to use it in Firefox browser too. At the moment stabile version of Java application recommended by the Bank is Java 7 Update 21. Upon new version of Java application launch please do not update before compatibility with eBanking application is confirmed – you will be informed about this in a due course. Cordially Yours Eurobank eBankin team.

I hope that translation is accurate and useful to others.