In case you encounter the mysterious net::ERR_CONTENT_LENGTH_MISMATCH error (doesn't apply to Firefox) let me guess: Using TYPO3 6.2.x? Using EXT:vhs? Thought so. The error can be caused by vhs' assets feature in the current TER version 1.8.5 and in combination with config.enableContentLengthHeader which is enabled in TYPO3 6.2 by default. So to fix it either disable config.enableContentLengthHeader (uncool) or use the current dev branch of vhs found on GitHub.