There is no option in
about:config to start firefox in fullscreen.
You can try to edit the
localstore.rdf file in the Firefox profile folder and find the section with
browser.xul#main-window and add/change the
<RDF:Description RDF:about="chrome://browser/content/browser.xul#main-window" height="843" width="1145" screenX="527" screenY="19" sizemode="fullscreen" />
To access Firefox profile folder, type
about:support on addressbar and find option to view the folder under Application Basics section. The option may be "Show Folder" (Windows), "Open Directory" (Linux) or "Open Containing Folder" depending on OS and version of firefox.
Close firefox before editing the file. Otherwise the change will be reverted.
NB: The original author of this answer disclaims that he/she is not sure about its working on Mac.
Another way is to edit the
xulstore.json file as described here: https://gist.github.com/hoangtranwork/fbd308f326a741109f8eb03a9990a839
Get the profile folder location in
Edit the file
xulstore.jsonfound in the above folder. It's a json file and we need only to edit the key
main-windowto something like this:
- Step 2 should be done when Firefox is not open, as it seems that the file get updated when Firefox closes.
- Sometimes you need to put negative value to
screenX if the windows is still shifted abit from the screen edge.