Forum:Cannot import large files

I try to use my wikia's import page: http://he.judaism.wikia.com/wiki/Special:Import to import an XML file about 680 KB large, but after I click "upload" I get a blank page, with a strange favicon (the favicon in Firefox looks like an airplane...)

It happens with other files too; I can only import very small files (about 20 KB or less).

What is the problem?