Browser s compatibility

Hello, when I started I didn’t know about the problem, so I first created my site for the IE 7 which I use. Result: FireFox doesn’t see the styles (CSS) – everything is white and too ugly. Opera applies the style but differently of course, so need a correction.
Now I want to correct the error but since FireFox doesn’t see my CSS style at all, how do I amend it? FireFox should be able to see and apply CSS, no?
Well, if someone could give a hint I’d be very grateful!
Thanks in advance.

What's the URL of your site?

I'm guessing that you're probably using conditional comments around your stylesheets, but without seeing the site it's difficult to know what the problem might be.

I would like to start using conditional comments but for the moment it is not the case since Mozilla doesn't show ANY reaction to my styles, so I don't know how to amend the CSS for it, so I haven't started yet.
Thank you so much for your time!!!!!!

I believe the problem is also related to your character encoding problem. Although you specify utf-8 in the meta data, your server is sending the content as utf-16LE. Viewing the page source with Firebug I can see some odd characters around the stylesheet links.

If you correct the encoding problem by adjusting the server to send the content as utf-8 it should correct the CSS issue as well.

Try W3's validator:

Style sheets: http://jigsaw.w3.org/css-validator/
Web page: http://validator.w3.org/

Fix any errors that come up when you check your webpage.

Thank you JagNet, could you tell me how to adjust the server? Should I contact my hoster?

And if it doesn't work can I do the vice-versa: adjust the meta data to utf-16le? Would it work then?

Thank you for the addresses, I have no errors.