I'm guessing that the "s" is an "accesskey" set in the page. To avoid confusion between menus and accesskeys on Windows, Firefox requires you to add Shift for accesskeys. In other words, Alt+Shift+s should trigger it. This can be changed to not require Shift. However, I'm not sure what happens in that case, i.e., how is the menu conflict resolved?? Check out the following thread for more info and the steps to experiment with this setting: [https://support.mozilla.org/questions/930607 I want to save with <alt><s> in the program Exact Online. This function is not working.] Does that solve it?