Site hacked? Changing elements to greek.

However it works fine in firefox…

Then check settings in other browsers.

Have you tried:
– Flushing any caching plugins you might be running, as well as server and/or browser caches.
– deactivating ALL (yes all) plugins temporarily to see if this resolves the problem (plugin functions can interfere). If this works, re-activate them individually (one-by-one) to find the problematic plugin(s).
– resetting the plugins folder by FTP. Sometimes, an apparently inactive plugin can still cause problems. Also remember to deactivate any plugins in the mu-plugins folder (if you have created such folder). The easiest way is to rename that folder to mu-plugins-old.
– If that does not resolve the issue, try switching to the unedited default Twenty Fifteen theme for a moment using the WP dashboard to rule out any theme-specific issue (theme functions can interfere like plugins).

– If the all the above steps don’t help resolve the issue, then You need to start working your way through these resources:

• https://codex.wordpress.org/FAQ_My_site_was_hacked
• https://wordpress.org/support/topic/268083#post-1065779
• http://smackdown.blogsblogsblogs.com/2008/06/24/how-to-completely-clean-your-hacked-wordpress-installation/
• http://ottopress.com/2009/hacked-wordpress-backdoors/

Additional Resources:

• http://sitecheck.sucuri.net/scanner/
• http://www.unmaskparasites.com/
• http://blog.sucuri.net/2012/03/wordpress-understanding-its-true-vulnerability.html