Is it only the one site that you have a problem with ? are other sites ok ?

It looks ok for me. I am using Firefox 15.0a2 at the moment.

First of all check the obvious:

• Do you just need to zoom in on that site (Use Ctrl + +) { the Keys Control and the plus symbol).
• Try clearing the cache and the cookies for that site, it may be just a temporary problem.
  • see also websites look wrong or appear differently than they should

Well, on all sites I see smaller text, than it was when I was using FireF 8.x, but on this site text is much more smaller. I try not to use "Ctrl + +" because I need to see orginal size. Hmmm Allways when i was installing new Firefox a have to change the valiue of font size from 16 to 17, and the problem was missing, but now changing the font size do nothing.

The site uses style="font-size: x-small;" for some text.
Firefox renders that with 10px size.

You can use an extension to set a default font size and page zoom on web pages.

• Default FullZoom Level: https://addons.mozilla.org/firefox/addon/default-fullzoom-level/
• NoSquint: https://addons.mozilla.org/firefox/addon/nosquint/

Thanks. Now I can see the difference betwen x-small and xx-small font size. The only remained problem is that "NoSquint" addon zoom whole text site - also menus etc.

You would need to apply a custom stylesheet (e.g. via userContent.css or Stylish) if you only want to change the font size of some elements.

@-moz-document domain(podkarpacka.ohp.pl){
span[style="font-size: x-small;"] { <your style rules> }
span[style="font-size: xx-small;"] { <your style rules> }
}

Now I've got everything.

Thanks Mate.