Make firefox white flashes in new tab loading screens go away

gistfile1.txt

Use this or https://github.com/overdodactyl/ShadowFox

How to make firefoxes white flashes in new tab loading screens black
Working as of firefox version 69 and 8th september 2019

Enable legacy css customisations
* Go to about:config
* Enable this flag:
`toolkit.legacyUserProfileCustomizations.stylesheets`

Get current profile directory from firefox: 
* Go to about:support
* Open profile directory

Create these directories/files if they don't exist

==================================================================

Create this file:
<profile_directory>/chrome/userChrome.css


@-moz-document url(chrome://browser/content/browser.xul) {
	#main-window,
	browser[type="content-primary"],
	browser[type="content"],
	tabbrowser#content,
	#content,
	browser[type="content"]>html {
		background: #181A1B !important;
	}
}

:root {
	--in-content-page-background: #181A1B/*tab flash on new tab*/
}


/*changes "flash" on tab open color*/

#browser vbox#appcontent tabbrowser,
#content,
#tabbrowser-tabpanels,
browser[type=content-primary],
browser[type=content]>html {
	background: var(--in-content-page-background)!important
}

.browserContainer {
	background-color: #181A1B !important;
}

==================================================================

And this file:
<profile_directory>/chrome/userContent.css


@-moz-document url-prefix(about:blank),
url-prefix(about:newtab) {
	html:not(#ublock0-epicker),
	html:not(#ublock0-epicker) body,
	#newtab-customize-overlay {
		background: #181A1B !important;
	}
}

@-moz-document url(about:newtab),
url(about:home) {
	body {
		background-color: #323234!important;
		color: #D1D1D1!important;
	}
	.card,
	.prefs-pane .sidebar {
		background-color: #202020!important;
	}
	#snippets,
	.section-title,
	.snippetContainer {
		color: #AEAEAE!important;
	}
	.contentSearchSuggestionTable,
	.contentSearchSuggestionsList {
		color: black!important;
	}
	.display-item {
		color: #D1D1D1!important;
	}
	#aboutMozilla::before {
		filter: invert(100%)!important;
	}
	#searchText {
		background: #474749!important;
		border-radius: 4px;
		border: 1px solid #262627;
		box-shadow: none;
	}
	#searchSubmit,
	#launcher {
		display: none!important;
	}
}

==================================================================
And then:
pkill firefox

And restart firefox

userChrome.css

/* Create and place in <profile_directory>/chrome/userChrome.css */

@-moz-document url(chrome://browser/content/browser.xul) {
	#main-window,
	browser[type="content-primary"],
	browser[type="content"],
	tabbrowser#content,
	#content,
	browser[type="content"]>html {
		background: #181A1B !important;
	}
}

:root {
	--in-content-page-background: #181A1B/*tab flash on new tab*/
}


/*changes "flash" on tab open color*/

#browser vbox#appcontent tabbrowser,
#content,
#tabbrowser-tabpanels,
browser[type=content-primary],
browser[type=content]>html {
	background: var(--in-content-page-background)!important
}

.browserContainer {
	background-color: #181A1B !important;
}

==================================================================

And this file:
<profile_directory>/chrome/userContent.css


@-moz-document url-prefix(about:blank),
url-prefix(about:newtab) {
	html:not(#ublock0-epicker),
	html:not(#ublock0-epicker) body,
	#newtab-customize-overlay {
		background: #181A1B !important;
	}
}

@-moz-document url(about:newtab),
url(about:home) {
	body {
		background-color: #323234!important;
		color: #D1D1D1!important;
	}
	.card,
	.prefs-pane .sidebar {
		background-color: #202020!important;
	}
	#snippets,
	.section-title,
	.snippetContainer {
		color: #AEAEAE!important;
	}
	.contentSearchSuggestionTable,
	.contentSearchSuggestionsList {
		color: black!important;
	}
	.display-item {
		color: #D1D1D1!important;
	}
	#aboutMozilla::before {
		filter: invert(100%)!important;
	}
	#searchText {
		background: #474749!important;
		border-radius: 4px;
		border: 1px solid #262627;
		box-shadow: none;
	}
	#searchSubmit,
	#launcher {
		display: none!important;
	}
}

userContent.css

/* Create and place in <profile_directory>/chrome/userContent.css */

@-moz-document url-prefix(about:blank),
url-prefix(about:newtab) {
	html:not(#ublock0-epicker),
	html:not(#ublock0-epicker) body,
	#newtab-customize-overlay {
		background: #181A1B !important;
	}
}

@-moz-document url(about:newtab),
url(about:home) {
	body {
		background-color: #323234!important;
		color: #D1D1D1!important;
	}
	.card,
	.prefs-pane .sidebar {
		background-color: #202020!important;
	}
	#snippets,
	.section-title,
	.snippetContainer {
		color: #AEAEAE!important;
	}
	.contentSearchSuggestionTable,
	.contentSearchSuggestionsList {
		color: black!important;
	}
	.display-item {
		color: #D1D1D1!important;
	}
	#aboutMozilla::before {
		filter: invert(100%)!important;
	}
	#searchText {
		background: #474749!important;
		border-radius: 4px;
		border: 1px solid #262627;
		box-shadow: none;
	}
	#searchSubmit,
	#launcher {
		display: none!important;
	}
}

Thanks for sharing this. Eases the pain.

@azraelle don't think so. Try using Shadowfox