This page will show you how to use the command line to start Firefox with a specific window size.
The following command is an example of, how to start Firefox with a specific window size of 1200×1200 and open the homepage of Firefox. This is a fine size for screenshots.
$ firefox -width 1200 -height 1000 https://www.mozilla.org/en-US/firefox
This page was last updated 2022-01-06.