Rated 5 out of 5 stars

Works perfectly fine! Read the info and it says the shortcut for Macs is different than for Windows, so pay attention. I didn't notice that the font size setting was at the bottom of the general add-on info because it was so small, but after a few moments of confusion about "What? But there's no settings button on the settings page!" I noticed it.

I have to use this kind of thing for basically every single site I ever go on, because I'm almost blind, so I really want to thank you a lot. There's other add-ons that do similar things but they're either broken or are a packaged deal and I don't want the package.

Rated 1 out of 5 stars

It doesn't do anything even with Options/Content/Advanced set to override page test font and size.

You need to choose a page with very small font to see an effect.
Don't forget to press Ctrl+Shift+0 after installing add-on.

Doesn't work Rated 5 out of 5 stars

Great, just what I was looking for. Unfortunately CTRL-SHIFT-O doesn't work. Using Firefox 28 beta.

Not letter O, it's number zero key.