Here is what I see in the console of Firefox 31 in the above URL:

"Exception thrown by user callback" load.php:10896
"[Exception... "Node cannot be inserted at the specified point in the hierarchy" code: "3" nsresult: "0x80530003 (HierarchyRequestError)" location: "<unknown>"]" DOMException [HierarchyRequestError: "Node cannot be inserted at the specified point in the hierarchy"
code: 3
nsresult: 0x80530003
location: https://bits.wikimedia.org/pl.wikisource.org/load.php?debug=true&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=20140812T191311Z:5732] load.php:10902
log() load.php:10902
handlePending() load.php:11894
runScript/markModuleReady() load.php:11991
runScript/nestedAddScript() load.php:11998
runScript/nestedAddScript/<() load.php:12003
jQuery.Callbacks/fire() load.php:3119
jQuery.Callbacks/self.fireWith() load.php:3231
done() load.php:9275
.send/script.onreadystatechange() load.php:9796

Created attachment 16182
Screenshot from Firefox 31

(In reply to wieralee from comment #0)

http://zapodaj.net/9ce0719ce726f.png.html

That's all we can see.

How many people have seen this problem?

Cannot reproduce error console output or how it looks.

Attached:

wieralee wrote:

From 21:30 till today morning bug existed for anyone who used Mozilla, IE or Chrome. Only Opera was without the bug.

We were talking about it on IRC. I was yesterday evening on your IRC channel, but nobody had answered. So I'd reported a bug here. Helder has checked & had the same bug.
He wrote me that is's java bug.

But today morning it's fixed. Thanks.

Yeah, I believe that. Just wondering what happened to create the problem and to make it go away again. :-/

In any case, I'm glad to hear it works for you again. And please reopen this ticket if this problem happens again.

I've deployed the fix for this yesterday: https://gerrit.wikimedia.org/r/153027

Ah, thanks!