I am getting the “This page is in Quirks Mode. Page layout may be impacted. For Standards Mode use “”.” warning in Firefox from a Wordpress site. The site uses <!DOCTYPE html> at the very top of the template html but of course all the wordpress config, plugins etc. are loaded before that. The error is not showing Chrome. How do I resolve this warning?
The “Quirks Mode” warning in Firefox typically indicates that the browser is rendering the page in a non-standard mode due to inconsistencies in the HTML structure or missing elements. Here are some steps you can take to resolve this issue on your WordPress site:
1. Check for Output Before DOCTYPE
Make sure that there is absolutely no whitespace or any other output before the <!DOCTYPE html> declaration in your main template file (usually header.php in a WordPress theme). Any space, newline, or character before the DOCTYPE can trigger quirks mode.
2. Disable Plugins
Temporarily disable all plugins to see if one of them is outputting content before the DOCTYPE. If the warning disappears, enable the plugins one by one to identify the culprit.
3. Check Theme Files
Examine other theme files, particularly functions.php or any custom templates, for any output (like echo statements, var dumps, etc.) that may be occurring before the DOCTYPE.
4. Look for Incorrect HTML Structure
Validate your HTML to ensure that it adheres to standards. You can use tools like the W3C Markup Validation Service to check for any markup errors that could cause rendering issues.
5. Inspect the Source Code
View the source code of your page in Firefox (right-click > View Page Source) and check for any unexpected output before the <!DOCTYPE html>.
6. Review wp-config.php
Check your wp-config.php file for any output before the <?php tag. It should start with <?php immediately, without any whitespace or new lines.
7. Check for Unclosed Tags
Ensure that all HTML tags are properly closed. Unclosed tags can also cause rendering issues.
8. Server Configuration
Sometimes, server configurations can inadvertently add output. Check your .htaccess or server settings to see if there are any directives that might affect output.
9. Browser Cache and Cookies
Clear your browser cache and cookies in Firefox, as cached versions of your site might display issues incorrectly.
10. Testing in Safe Mode
If the issue persists, try switching to a default WordPress theme (like Twenty Twenty-One) and check if the warning still appears. This can help determine if the issue is theme-related.