Hi there.

This is the general structure of my extension:

1. A background_page called background.html
2. No popup
3. Permissions [ "tabs", "http://*/*" ]
4. The background page uses chrome.tabs.executeScript to inject the content script into the page (from inside a browserAction.onClicked listener)
5. It has an onRequest listener. The request is fired from the content script. The listener sends a response to the content script in the end. The content script then uses this response to change the respective page

Now my problem:
The content script has grown bigger and bigger over time and now I seem to have reached some limit ... even if I just add comment lines, it will not execute any more. There is no error (as far as I can see), but it just won't execute any more.

Is there a size limit for content scripts injected using executeScript?

I haven't heard of one. Have you tried splitting up you content script into multiple files and injecting them?
Also, why not just use the content_scripts section in the manifest to inject them, and send a message to the background page from the base level of the script? If you need the tab info, that's sent with the message when it's a content script.

I use the content_scripts section of the manifest now. But no luck on my first try.

Then I removed line by line and identified the problem: One line of the code had a special character inside a comment(!) and Chrome stopped working without complaining. I think I will have to switch to UTF-8 even if I use special chars only in comments ...