I would like to reset the size and placement of Firefox, but I do not want to run a full Refresh of my settings. You can no longer just run window.resizeTo in newer versions of Firefox to just manually set the size anymore.
You can reset the window size for Firefox back to its default settings by deleting the
xulstore.json file. It can be found in the root of your Firefox profile folder. You will need to make sure that Firefox is not running when you remove this file.
On Windows Firefox's profile folder can usually be found in the following location: