Hmm, that's strange!

First, where you do see that message?

Second, why do you have this jQuery extension installed: https://addons.mozilla.org/firefox/ad.../jquery/?

1. on one of sites 2. to try resolve a problem thanks 4 answer)

I suggest disabling that jQuery extension.

If that site is http://lexauto.ru/ it calls jQuery as follows (found in the source view):

<script type="text/javascript" src="http://yandex.st/jquery/1.7.2/jquery.min.js"></script>

Maybe yandex.st is blocked on your Firefox for some reason.

disabled, but the message is still shown. Where can I see if yandex.st is blocked on my mozilla?

After OK'ing the error, open the Web Console using either:

• menu > Developer > Web Console
• Ctrl+Shift+k

This should appear in the lower part of the tab. Then reload the page and Firefox should start accumulating information in the console. You can OK the error again, then scroll up the console to see whether there are any error messages that could explain while the file was not retrieved.

You also could click to the Network Monitor (click Network along the top bar of the Web Console). This lists all the requests generated from the page. Does the jQuery request show anything different from the others?