I used your link and had no problem.

https://support.mozilla.org/en-US/kb/server-not-found-connection-problem

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

http://kb.mozillazine.org/Error_loading_websites

Thanks for refs to articles; however, I've already read them (before posting my question). The problem persists: www.rutracker.org cannot be loaded in Mozilla, but is loaded in other browsers; this site is loaded in Mozilla too, but in other user account (on the same PC). When browsing to http://www.rutracker.org, Mozilla is referred to http://www.rutracker.org/forum/index.php, then the connection cancels. It had been working for a long time, but stopped working several months ago. No security exception is added. I've no idea.

Thanks in advance

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

Restarted in the safe mode, the problem persists. After switching to http://www.rutracker.org/forum/index.php, connection is cancelled.

As a test, disable your protection programs and try again.

The only my virus-protect program is AVG. I switched it off for 10 mins, and tried to connect http://www.rutracker.org in Mozilla. Result is the same. Other browsers (and even Mozilla in other user account) can connect http://www.rutracker.org, so (IMHO) it doesn't seem that the reason is related to some external programs.

I've called the big guys to help you. Good luck.

Waiting. Thanks for your trying to help.

Try a new profile to make sure the cache is not corrupt. Since its working on another computer and network we know its not the website.

• Profile Manager - Create, remove or switch Firefox profiles

guigs2, many thanks. In another profile of Mozilla the site rutracker.org is launched with no problem. It was predictable, because it works in Mozilla from another windows user. Of course, it is possible to delete my main profile and use new one (or reinstall Mozilla). However, it cancels all my profile preferences. So, the question persists: is it possible to fix my main profile?

Thanks for help

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

These can't get your data back, but will help in the future.

These add-ons can be a great help by backing up and restoring Firefox

FEBE (Firefox Environment Backup Extension) {web link} FEBE allows you to quickly and easily backup your Firefox extensions, history, passwords, and more. In fact, it goes beyond just backing up -- It will actually rebuild your saved files individually into installable .xpi files. It will also make backup of files that you choose.

OPIE {web link} Import/Export extension preferences

FredMcD, thanks for an interesting add-on. IMHO, it is 95% probability that the problem will be restored along with back-upped and restored things. Anyway, this addon can be useful in future.

I've managed to settle the problem: it has appeared to suffice to delete cookies related to rutracker.org. It is interesting, that I tried to switch off all add-ons and even to clean profile, but it doesn't work.

Thanks everybody who tried to help