User Agent: Mozilla/5.0 (Windows NT 6.1; rv:50.0) Gecko/20100101 Firefox/50.0 Build ID: 20161210192100 Steps to reproduce: 0) Firstly open firefox's option and at the general tab make sure multi-process is enabled. 1) Open http://forums.mozillazine.org/viewforum.php?f=9 2) Scroll to the bottom and click on the <select> element, so the dropdown popup show up. 3) Press Ctrl++ to zoom in the page and observe the font size of the dropdown popup. 4) Right-click the <select> element and click "Inspect Element" at the context menu. 5) Add "font-size: 18pt" style to the <select> element. 6) Click on the <select> element again to show the dropdown popup. 7) Check if the font size of the dropdown popup changed. Actual results: When zoom in the page the font size of the dropdown popup do not change. After adding "font-size: 18pt" style <select> element, the font size of the dropdown popup remain unchanged. Expected results: Font size of dropdown popup should change accordingly when zoom in the page. Font size of dropdown popup should change accordingly when change the font size of <select> element.