There might be an extension for this on the Add-ons site but if you don't find one, you can apply a custom style rule to the sidebar.

That area can be changed to a white background using this rule, for example:

#bookmarksPanel, #history-panel {
  background-color: #fff;
}

Applying custom style rules to the browser UI area can be done in either of two ways:

(1) Using the Stylish extension (2) Creating/editing a userChrome.css file

It's really late for me here, so I can't go into all the details, but there is hope!

See also this thread:

• [/questions/1060221]

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 */

#sidebar-header,#sidebar-search-container,#bookmarks-view-children,#historyTree {
color: #000 !important;
background-color: #fff !important;
-moz-appearance:none!important;
border-color:transparent !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

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

• Create the chrome folder (lowercase) in the <xxxxxxxx>.default profile folder if this folder doesn't exist
• Use a plain text editor like Notepad to create a (new) userChrome.css file in the chrome folder (file name is case sensitive)
• Paste the code in the userChrome.css file in the editor window
• Make sure that the userChrome.css file starts with the default @namespace line
• Make sure that you select "All files" and not "Text files" when you save the file via "Save file as" in the text editor as userChrome.css.
  Otherwise Windows may add a hidden .txt file extension and you end up with a not working userChrome.css.txt file

Got it! My eyes thank you for your help!