Firefox 45 has introduced a regression where responsive images with the
srcset attribute, introduced with Firefox 38, fail to get updated when the attribute value is programmatically changed in a certain way. This bug is affecting product image display on WooCommerce-powered online stores. Mozilla developers will be working on the solution.
Update: Our analysis has found that this bug affects the YITH WooCommerce Zoom Magnifier plugin that has 90,000+ active installs.
Update: Firefox 45.0.2 has been patched, but the QA team reports that the issue is still rarely reproducible. Mozilla developers are investigating the cause.