MIME type error - Refused to apply style / Refused to execute script. Strict MIME checking is enabled

Symptom:
Refused to apply style / Refused to execute script due to Strict MIME checking.

This usually occurs when Magento hasn’t generated static content correctly. It can also appear on a vanilla Magento install and isn’t necessarily related to a theme or extension.

In most cases, the error disappears after setting correct permissions and regenerating static content.

Solution 1 — Fix permissions, switch modes, and deploy static content

1. Set correct Magento permissions

Follow the Basic Permissions Setup guide:
https://help.weltpixel.com/en/article/how-to-set-magento-2-permissions-and-avoid-installation-errors-ufa03p/?bust=1758010804465

2. Switch to Developer mode, then to Production mode

This cleans caches, compiles code, and generates static content:
https://help.weltpixel.com/en/article/how-to-set-magento-2-developer-and-production-mode-via-ssh-a2vjwi/?bust=1758010825880

3. Deploy static content for each locale (if you use locales other than en_US, e.g., nl_NL, en_GB)

Example command (run from Magento root):

php bin/magento setup:static-content:deploy -f en_GB

If the error persists, there may be an issue with missing .htaccess in pub/static.

Solution 2 — Restore missing .htaccess in pub/static

1. Navigate to:

pub/static/

2. Check for .htaccess (it’s a hidden file; press Ctrl+H in many file managers to reveal).
3. If missing, copy the version-appropriate .htaccess file into pub/static/ from your Magento source for your exact Magento version.
4. Clear caches and retest:
5. • Clear browser cache
   • Clear Magento cache

Why this works

• Permissions & ownership ensure the web server can write static assets.
• Mode switch + static deploy rebuilds static files with correct headers and paths.
• .htaccess in pub/static sets proper MIME types and routing rules required by Magento’s static content server.

Updated on: 16/09/2025