Hi WendyB, I see that in a different PDF as well (comparison attached). When I look in Acrobat, there are innerable little elements being drawn in the page and possibly some of the positioning isn't being interpreted the same way for some reason. Is there any possibility of merging the graphical elements together into a single image so there are fewer individually positioned bits and pieces? Since this problem affects the pdf.js project that Firefox uses to render PDFs -- even testing in the latest version of the viewer available at [https://mozilla.github.io/pdf.js/web/viewer.html] -- you may want to file an issue on their Github repository: https://github.com/mozilla/pdf.js/issues/