Insert Media, Hyperlink and so on, doesn't work in Firefox

Don't know what has happened here but lately I can not insert any images, hyperlinks or other stuff into a post when using Firefox.
Nothing happens when I click the buttons to insert Media or Smilies, and if I click Paste from Word, Insert/Edit Link or Insert New Table for example, I get a white ribbon across the screen with a text saying something like "{#table dlg.title}".
Anyone else seeing this?

Using Windows 8.1, 64-bit and Firefox 34.0

Working fine when doing the same thing from Internet Explorer.