Go to the Mozilla Add-ons Web Page. There’s a lot of good stuff here.

I have looked there. I can't swear that none of the add-ons can control background but I couldn't find one for Android. My mother is partially-sighted and controlling the contrast of text on websites is crucial. It's simple on regular firefox but frustratingly not present on the android version.

Okay, let's try Firefox Options > Content. Then check out Fonts and Colors. Don't forget to check out the Advanced and Colors buttons.

I have the latest FF for this nexus 7 tablet android. There are settings, but not options or options->content that you get on the standard FF for a PC.

Check out NoSquint and see if you can use it.

Nosquint only works on desktop Firefox. You can check what versions of Firefox an addon supports by clicking on the version information at the bottom of the extension listing. If Firefox for Android is not listed then it won't work without changes by the addon developer.

Hi Jeffbrandes, is it something you will need to change often?

Assuming not, you can manually change these settings in the about:config interface on mobile Firefox the way you can on desktop Firefox. (If you try other preferences and they do not work, probably they are not implemented in mobile.)

I suggest you first change your desktop Firefox to the desired foreground and background color. This will help you discover the color codes you will need.

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the search box above the list, type or paste color and pause while the list is filtered

You should see that these two preferences are bolded, indicating they have changed from their defaults:

• browser.display.background_color
• browser.display.foreground_color

Keep this page handy for reference. On your mobile, tap the address bar and type about:config and tap the Go button or the Enter key.

In the search box, type color and tap the Enter key.

Scroll down to the preferences you want to modify, tap the Modify button, then enter the code you see in your desktop version of Firefox for the corresponding preference.

IMPORTANT: If you are reversing the colors completely, e.g., going from white on black to black on white, choose an intermediate background color such as a medium green (#33CC00) for the first change, otherwise you will not be able to see the preference names. If you forget, tap the enabled Reset buttons until you clear the change.

Note: If you like to play around with settings, I recommend bookmarking about:config.

Sorry, you wrote colour (British spelling) and if you have a British Firefox, that might also be used in the preferences. I'm not sure.

Forgot one. To override page colors, you need to Toggle (switch from true to false) this preference that should have come up in your color search:

browser.display.use_document_colors

Thanks guys, not an ideal solution but very useful info.