You could use the userContent.css to set a CSS rule for that domain. You would have to check via the Inspector what selector(s) you need to use on each website (#id or .classname).

• https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Getting_started/Selectors
• https://developer.mozilla.org/en/CSS/@document

• https://developer.mozilla.org/Web/CSS/white-space
• https://developer.mozilla.org/Web/CSS/word-break
• https://developer.mozilla.org/Web/CSS/word-wrap

@-moz-document domain(<domain>){
 selector { white-space:normal!important; word-wrap:break-word!important; }
}

See:

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

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

• 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) userContent.css file in the chrome folder (file name is case sensitive)
• Paste the code in the userContent.css file in the editor window
• 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 userContent.css.
  Otherwise Windows may add a hidden .txt file extension and you end up with a not working userContent.css.txt file

Well month past -I found setting! I appreciate the response. I played with the suggested workarounds for several hours with some very limited results (none really solving but learned a bit). I gave up -mostly not knowing what the heck I was doing. Was becoming more effort than clicking on page display & turning off word wrap :), thinking I'd get back to it... Then Mozilla upgraded... Searching for more critical fixes (firefox memory usage just keeps climbing) stumbled on a few ideas, still working on that. However one suggestion led me into about:config. Opening another tab & looking thru the list found plain_text.wrap_long_lines default boolean true I double clicked on it (or right click and select toggle) changed it to plain_text.wrap_long_lines user set boolean false WALA! Default page view for text is now 'Basic Page Style' not 'Wrap Long Lines'. Turning on word wrap is now the option. Cool. For viewing long data fields- nice. No more menu-View-Page Style-Basic Page Style repeatedly during session.