Help with setting Firefox download preference

[aakash3771]

Below are the FF preferences. When I download a file, it downloads to my default downloads folder on my machine. I need firefox to download into the downloads folder in nightwatch repo. I don't know why these prefs are not helping. Could someone please help with the prefs

"firefox": {
"desiredCapabilities": {
"browserName": "firefox",
"javascriptEnabled": true,
"acceptInsecureCerts": true,
"nativeEvents": true,
"moz:firefoxOptions": {
"log": {
"level": "trace"
},
"args": ["-headless", "-no-remote"],
"prefs": {
"pdfjs.disabled": true,
"browser.download.folderList": 2,
"browser.download.dir": "./downloads/",
"browser.helperApps.neverAsk.saveToDisk": "application/pdf",
"browser.download.manager.showWhenStarting": false,
"browser.helperApps.neverAsk.openFile": "application/pdf",
"browser.helperApps.alwaysAsk.force": false,
"browser.download.forbid_open_with": true,
"browser.download.manager.useWindow": false,
"browser.download.manager.scanWhenDone": false,
"browser.download.manager.focusWhenStarting": false,
"browser.download.manager.showAlertOnComplete": false,
"browser.download.manager.closeWhenDone": true,
"browser.cache.disk.enable": false,
"browser.cache.disk.capacity": 0,
"browser.cache.disk.smart_size.enabled": false,
"browser.cache.disk.smart_size.first_run": false,
"browser.sessionstore.resume_from_crash": false,
"browser.startup.page": 0,
"media.navigator.streams.fake": true,
"media.navigator.permission.disabled": true,
"device.storage.enabled": false,
"media.gstreamer.enabled": false,
"browser.startup.homepage": "about:blank",
"browser.startup.firstrunSkipsHomepage": false,
"extensions.update.enabled": false,
"app.update.enabled": false,
"network.http.use-cache": false,
"browser.shell.checkDefaultBrowser": false
}
}
}
}