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Customers using Internet Explorer 11 and also Microsoft Edge's IE11 Compatibility Mode might encounter various issues with loading pages with lots of CSS. This article documents one performance limitation and one known issue with a workaround.
Resolution
Performance Limitation
Performance issues have been encountered due to the amount of times IE11 executes multiple style recalculations on pages with lots of dynamic CSS styling. This performance issue has been recognized by Liferay Support as a possible known issue as well. Unfortunately, this is a Microsoft issue and customers should consult Microsoft's documentation for a solution.
For more information, see this article: Microsoft Internet Explorer 11 Performance Issues Due to CSS Style Calculations.
Known Issue
By default, the Liferay platform enables CSS merging to allow for faster load times. (CSS merging refers to the ability to combine multiple CSS style sheets into one for faster load times.) However, Internet Explorer 11 (IE11), with Compatibility Mode enabled, may not be able to properly render CSS-merged pages, thereby leading to greatly increased page load times.
One workaround is to disable CSS fast loading by setting theme.css.fast.load=false in your portal-ext.properties. Please note that this will lead to slower load times on other browsers that can properly handle CSS merging.
Also note that Internet Explorer's Compatibility Mode is not supported in any version of the Liferay platform. Please see footnote #4 under Desktop Browsers in this Support Coverage article.