MIME Type Conflict With TYPO3 Compressed CSS And JS Resources

- 1 answer

I am rather new to TYPO3. Recently I noticed some very weird behavior in my installation: Some CSS-files in the directory typo3temp/assets/compressed got the MIME-type text/html instead of the expected text/css. Therefore my browser received a 403 Forbidden status code from the webserver for these resources. That resulted in some parts of the backend being shown without styling.

I tried clearing all caches and deleting the typo3temp/assets/compressed directory, however now all the stuff in there (CSS and JS) is served with MIME-type text/html. Getting the backend without JavaScript means, that I am now basically locked out of the backend. I can however still reach and use the install tool.

Do you have any ideas how this might happen and how to fix it?

Some details of my setup:

  • TYPO3 v10.4.13 (recently updated from 10.4.9)
  • Apache web server (I don't have access to its config and have to rely on .htaccess files)


I suggest to set


in order not have these kind of problems. The problem is that this compression creates compressed files but relies on webserver configuration in order to deliver them as text/css and NOT applying the default webserver's transport compression to them (or they could end up double-compressed and you might not even easily notice - some browsers can deal with that, others not).

It is a kind of micro-optimization that sounded useful in times when we avoided https:// because of the processing overhead...

Here's some docs (the first statement is outdated in my oppinion):