In my FM19 document I have a table with the same width as the FM page (same as the pdf ouput.)
But in the html5 output, the table has a fixed width too. This looks weird, especially when the browser window is much wider. Can I somehow make the table with dynamic, so it always fits the page width?
Try editing the CSS used for your HTML5 conversion.
You can manage that CSS by using Import and Export options in the Publish Settings dialog.
Strange, I can't even find the table style in the css file.
Ah, but now that you are in there, you can add CSS to control your tables
(or, you can economically have someone write that CSS code for you, using fivrr.com or other services)