2018
I think it's easier on my eyes to have white print on black background. I tried an add-on that just darkens the browser windows, but that's just similar to the brightness adjustment on the computer.

Inverting the webpage colors changes most black-print on white-background to white-print on black-background, which is much less like staring at a light bulb. (It doesn't work on addons.mozilla.org.)

And then, if you throw in color content, the result of color inversion is a little psychedelic. I like it.

The add-on adds a little icon in the toolbar. So it's easy to turn the inversion off and on with a quick click.

2019
Thanks to the add-on author, Max, for replying to my review. Max wrote:
> Firefox does not allow plugins to alter addons.mozilla.org pages for security reasons.

True. That's Firefox's problem :) And it's a real problem with their ALL WHITE PAGES that need color-inversion as much as anybody.

I came back to add to my previous review. One option that Invert-Colors provides is to invert-colors on the whole page -- "Except For Graphics." This is genius. For instance, you can turn eBay, which is as bright-white as any website, and turn all that white into black -- without changing the graphics of the items, if you select the option! Very groovy.

A month ago, a reviewer wrote:
> Does what it says, it inverts images witch I wish it didn't, it will also be disable when typing.

This reviewer needs to check out the options, which are located in the Add-Ons Manager. When you're on the Invert-Colors page, click on the Options tab at the top.

The reviewer also wrote
> it will also be disable when typing.
Say what? I started typing, which invokes the "Find" function in Firefox, and it did not disable Invert-Colors. Then I typed into eBay's search function, and that didn't disable Invert-Colors, either. Not on my Win7 lapotp.