[TYPO3-english] TYPO3 6.2.15: backend browser crashes (Firefox, Chrome) when opening plugin News with error "Unresponsive script"

[Bert]

Hello,

I am working with TYPO3 6.2.15 in the backend and intensively with the 
News plugin...

The backend responds fine except when opening the News-plugin (or any 
other content element): the browser (Firefox, Chrome) crashes with error 
"Unresponsive script"...and then "Network connection error"...

I am using php5.6 with Optcache enabled, sufficient memory allocated 
(300MB)...

Any idea where this comes from or how to debug further?

Any suggestion will be highly appreciated!

Thanks in advance.

Regards,
Bert