I noticed that a lot of cyrillic pages are missing glyphs. The blanks are so frequent that they prevent reading and understanding of those pages. Some of russian pages that originally display correctly when sent in mail (Page send...) are missing glyphs in the thread and message body.I thought that this is a font issue but would i lack proper fonts those chars would probably be displayed as question marks (????). So is it a converter problem? I'll attach a screen shot.

Duplicate of bug 162593? Does deleting components/compreg.dat help? (Exit all instances of Mozilla first).

this bug has nothing to do with bug #162593, this problem is on the branch and has been there for a while, it is not that encoding is broken and the page can not be rendered correctly, this is a possible converter problem.

It looks like you don't have any Cyrillic font installed on your system. All of Cyrillic letters in your screenshot were rendered with 'doubld width' glyphs from CJK fonts (that cover a subset of Cyrillic letters but not all of them). What do you get if you do 'xlsfonts |grep koi' or 'xlsfonts |grep 8859-5'. If you get nothing, it's definitely caused by the lack of any Cyrillic fonts on your system.

This seems like an issue specific to a particular installation and not relevant to current code.