Does this help;

Your zoom controls.

<Control> + (plus) enlarge <Control> - (minus) reduce <Control> 0 (zero) restore

I've called the big guys to help you. Good luck.

You can look at this extension to adjust the font size for the user interface.

• Theme Font & Size Changer: https://addons.mozilla.org/firefox/addon/theme-font-size-changer/

You can use an extension to set a default font size and page zoom on web pages.

• Default FullZoom Level: https://addons.mozilla.org/firefox/addon/default-fullzoom-level/
• NoSquint: https://addons.mozilla.org/firefox/addon/nosquint/

Can't I just change the font sizes of those indivisual elements I mentioned without making global changes?

I have changed layout.css.devPixelsPerPx from the default -1.0 to 1.0. I also added the following codes to userChrome.css:

   menubar, menubutton, menulist, menu, menuitem, textbox,
   toolbar, .tab-text, tree, tooltip, sidebarheader, statusbar {
   font-size: 11pt !important; }

Afterwards I'm OK with most of the UI elements.

Since the above style codes does work with individual UI elements (menubar, etc), I thought there might be codes that work with the Options dialog and the about:??? pages.

Correct me if I'm wrong.

You may have to use a lot of style rules to cover all possible windows including windows that open if you click a button like the Cookie Manager (#CookiesDialog) and the Password Manager (#SignonViewerDialog).

The Options/Preferences window has this ID: #BrowserPreferences (chrome://browser/content/preferences/preferences.xul)

#BrowserPreferences * { font-size: 11pt !important; }

Ah! I forgot there are other windows called from the main Options window... But I'm still very glad that the font size of the main Options window is now increased with the codes you provide. Major goal accomplished.

Thank you very much.

And... how about the small font sizes of the about:??? pages and the Help > Troubleshooting Information page? Is it possible to adjust for only those pages without affecting the global default font size setting of all pages? I have checked NoSquint. It can only make per-site exceptions from the default zoom levels it sets, but can not set level zooms for specific pages.

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support.

FredMcD said

If you haven't already, please select the answer that solves the problem.

Although now I can increase the font size of the main Options window, the same small font size problem with the about:??? pages and the Help > Troubleshooting Information page remains. (I have checked NoSquint, which can not set default zoom level for individual pages.) So I'd like to wait for a few more days before I select the answer.

The about:config page needs code in userContent.css for the font size.

/* about:config and about:support */
@-moz-document url(about:config), url(about:support){
 *{font-size:11pt!important}
}

All Problems solved!

There is a bonus... I add url(about:) and url(about:cache) to the userContent.css codes provided by cor-el, and they do work with those two extra pages. Sweet!

Thanks again.