I have the same problem. The bug is in the class “woocommerce-product-gallery__image” element. WordPress give a width value in chrome or safari (a coorect one), and other in firefox (here is the same width than the class “woocommerce-product-gallery”). I suppose it happens because I move the gallery thumbnails to the left of the main image. I don’t know how can I fix it.
Chrom:
<div data-thumb="https://dozeclean.local/wp-content/uploads/2020/08/CAM_15-150x150.jpg" data-thumb-alt="CAM_15" class="woocommerce-product-gallery__image flex-active-slide" style="width: 554px; margin-right: 0px; float: left; display: block;">
Firefox:
<div data-thumb="https://dozeclean.local/wp-content/uploads/2020/08/CAM_15-150x150.jpg" data-thumb-alt="CAM_15" class="woocommerce-product-gallery__image flex-active-slide" style="width: 633px; margin-right: 0px; float: left; display: block;">
