Firefox has numerous different context menus. Based on a post on the mozillaZine forums (link), these custom style rules will give three of them a white background:

@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);
#contentAreaContextMenu * {
    background-color: #fff !important;
}
#tabContextMenu * {
    background-color: #fff !important;
}
#placesContext * {
    background-color: #fff !important;
}

Custom style rules can be applied to Firefox using either a userChrome.css file (a file you create, or if it exists, that you edit, which is read by Firefox when it starts up) or using an extension such as Stylish.

To apply the rule using the Stylish extension, step 1 is to install the Stylish extension: https://addons.mozilla.org/en-US/firefox/addon/stylish/

Next, select and copy the rule from earlier in this post.

To set it up:

(1) Stylish will add an "S" icon either to the main Navigation Toolbar or to the Add-on bar. Click the Stylish "S" icon > Write new style > Blank style.

(2) Click in the large editing area next to the faded "1" and paste in the rule.

(3) Click the Preview button to apply the rule. Success?

(4) Before saving the rule, type a name in the top box, for example: Context Menus White BG

That's it. Unless there's a problem in Step 3.

Regarding other menus, is it the classic menu bar or the orange Firefox button menu? These have different CSS selectors (the hooks for applying style rules).

Is this in the Firefox user interface?

You can see if you can find a complete (full) theme that has a setting to change this color.

Add code to the userChrome.css file below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

menupopup { background-color: rgb(255,255,255) !important; -moz-appearance: none!important; }

The customization files userChrome.css (user interface) and userContent.css (websites) are located in the chrome folder in the Firefox profile folder.

• http://kb.mozillazine.org/Editing_configuration

@jscher2000 Unfortunately your code doesn't work for me but thank you anyway for your time. Moreover I'm so happy to learn about Stylish extension and I will play immediately with it.

@cor-el Thank you so much, you solved my problem, your code is perfect for my needs. Only a question, I ask you if this code will work for a long time or probably it will change in the future. Thank you also from my sister, the visually impaired person that moved me to ask your help.

You're welcome

This is a very generic code that only has a 'menupopup" selector that is very unlikely to get changed as this would involve to change all Firefox theme and CSS files that use this selector...

Perfect, this is a real good news, so I will have this setting for a long time. Thank you so much cor-el, you are a good man!