Problems with FOUC

Several solutions were offered in the Firefox and Redit forums for this problem. I am not sure that they all treat the same case, so you might as well try them all.

The post Firefox Quantum flashes white screen when idle tabs are clicked advises to edit or create in the profile folder the files userContent.css and userChrome.css and add in both the following line:

.tabbrowser-tabbox { background-color: #a9a9a9 !important; }

If the file(s) already exist, check that this does not conflict with existing content.

The post How can I make the color of newly opened (but unloaded) windows/tabs dark? advises to add in userChrome.css the lines :

/* Reduce the "white flash" in new tabs */
browser[type="content-primary"], 
browser[type="content"] {
  background: #778899 !important;
}

Check that this is not already done if you have installed ShadowFox (a universal dark theme for Firefox).

The post How do you stop firefox from flashing a white screen while a page is loading? advises in about:config to set browser.display.background_color to a darker color (#333). Also adding into userChrome.css :

{ background-color: #333 !important; } 

The post Removing the white flash before a page loads contains more code for userContent.css and userChrome.css, which may also already be contained in ShadowFox. The code is too large to include here.

If one of the above methods solved the problem, please indicate which one.