From the Firefox menu bar, select

     
Tools > Options > General 

and set your home page from there

I've tried that about a dozen times. No matter what, whatever is hijacking my homepage changes it back. Eventually it will start to destroy other webpages.

You may have a compromised HOSTS file. See
http://support.microsoft.com/kb/972034

You can add the entire telefonnyzoznam dot info domain to your Adblock list of blocked sites too.

You should visit the antivirus vendors Trend Micro, Norton, and others that have on-line scanners to check your system again.

After you know that your system is clean again,

• Use a program like Secunia's Personal Software Inspector (PSI) to help automate the process of updating all software on your computer.

• Install the NoScript extension in Firefox. (Follow the directions for training the extension to only run scripts on sites you want. If there are sites you use that have annoying behaviors, turn off their ability to run scripts until you go use the site, then turn them off again when you leave. )

To update your plug-ins, go to:

      https://www.mozilla.org/en-US/plugincheck/

edited to add adblock site

Neither Trend Micro or Norton off line searches found the problem. Nor did Norton Deep, etc. However in continuing the search I found HitmanPro35, ComboFix and Malwarebyte. One of these found it, after 5 hours of searches. All three work quickly, usually less than 10 minutes, but it took a while for them to root all all variations in back ups, etc. I also ran Malwarebyte and Norton in Windows Safemode which found some more issues. Great programs that went far and beyond what Norton, Trend Micro, etc found.