Preserving zoom level in Firefox

Question

Is there a way to preserve the zoom level attained by pressing Ctrl+ or Ctrl- in Firefox?

Let me be very specific about the issue at hand: I sometimes connect my laptop to an external monitor so I can browse with my wireless keyboard while lying on the couch. For that I need a higher zooom level, otherwise I can't read the letters on the screen as I'm further away than normal.

It's essential that I can change the zoom level with the use of keyboard only. I'm lying on the couch with my keyboard; getting up to do mouse stuff defies the purpose.

Ctrl+ /Ctrl- would be perfect if only the zoom level would be preserved but each time I open another tab it's back to default 100%.

Here's what I have tried:

• Changing the default zoom level in about:config. This requires Firefox to be restarted which I won't have to do just because I connect another monitor.
• Installing the plugin Default FullZoom Level which enables you to change the default zoom level without restarting. This requires you to go: Menu > Add-ons > Default FullZoom Level and entering a numeric value. I don't know how to go the add-on menu by means of keyboard only and even if I did it wouldn't be handy ...

When I press Ctrl+ a number of times I would like that to be the zoom level of all new sites I visit just up until I press Ctrl0. Can that be done?