Alt > View > Character Encoding = select it there

Thank you for your answer.

I have noticed that if I have many site pages opened at the same time (one at each Tab), changing the character encoding using View > Character Encoding = select one here, will only change the character encoding of the selected page (Tab) and not the others pages. So, doing that, I can define one specific character encoding for each selected page.

Then if I setup Firefox 4 to open all the last opened pages and then close and open Firefox 4 each page will have it's own character encoding. Is it correct?

Bring up the menu bar. Select 'Tools.' Go to the bottom of the popup menu and select 'Options.' On the window that pops up select the 'Content' tab. About halfway down the window you will see 'Fonts and Colors.' Select 'Advanced.' At the bottom of the resultant window you will see 'Default Character Encoding.'

Now the bad news: everything still shows screwed up because 'Unicode (UTF-8)' is still always selected on individual web pages. I dunno why.

If the server sends an encoding then Firefox will always switch to that encoding.
The default is only used on pages where the server does not send en encoding via the HTTP response header and the code doesn't specify the encoding via a meta tag.

There is usually no need to change the encoding from the default setting Western (ISO-8859-1).

It is probably better to try an Auto-Detect setting (e.g. View > Character Encoding > Auto-Detect > Universal) if you have a problem on specific websites.