How to prevent display color option settings from disappearing after a restart of Firefox?

Question

I like to display specific text, background and link colors overriding pages' defaults; that info disappears almost after every Firefox restart. These settings are set in: Firefox>Options>Options>Content>Colors and having to reset them almost every time I start F is a pain.
An ideal solution would be to allow a user to save their color picks as a separate "theme". I would then prefer to have 3 such saved themes that would be easy to switch at a push of a button:
1. Light text on dark background (dark screen, less contrast) for a dark room;
2. Lighter text on dark background (dark screen, more contrast) for a bright room;
3. Firefox default.
Finally, replacing a color palate with few colors with a color wheel from OS would be ideal and relatively simple to implement.
This may or may not be related but preferred magnification of text on each individual page is also often lost (reset to default).

Answer 1

See if the following article helps.
* [[How to fix preferences that won't save]]
Overriding web site colors may not be good idea because it also gets rid of background images. Some sites set background images for certain web page elements to display information that's crucial to using the site (like text for buttons).
You can use the Stylish add-on to manage user styles that change the appearance of web pages in various ways. You can click the Stylish toolbar icon and enable or disable styles that are applied to the current page.
# Install Stylish and restart Firefox when prompted.
#* https://addons.mozilla.org/firefox/addon/stylish/
# Click the ≡ Menu Button and choose Add-ons.
# In the Add-ons Manager, click User Styles on the left.
# Click the Write New Style button at the top. Paste the following in the text box, give the style a name, then click the Save button.
<pre><nowiki>
@-moz-document url-prefix("http://"), url-prefix("https://") {
/* Dark background and light text. For more color names, see http://www.w3schools.com/HTML/html_colornames.asp */
* { background-color: rgb(20,20,20) !important; color: whitesmoke !important; }
a:link { color: royalblue !important; }
a:visited { color: blue !important; }
a:hover { color: lightblue !important; }
a:active { color: red !important; }
}</nowiki></pre>
<pre><nowiki>
@-moz-document url-prefix("http://"), url-prefix("https://") {
/* Light background and dark text. For more color names, see http://www.w3schools.com/HTML/html_colornames.asp */
* { background-color: whitesmoke !important; color: rgb(20,20,20) !important; }
a:link { color: royalblue !important; }
a:visited { color: blue !important; }
a:hover { color: dodgerblue !important; }
a:active { color: red !important; }
}</nowiki></pre>
You can install the Rainbowpicker add-on to choose any color everywhere in the Firefox interface (like Options/Preferences - Content - Colors).
* https://addons.mozilla.org/firefox/addon/rainbowpicker/