Firefox zoom preferences

Firefox’s default zoom preferences are ok, but if you want what Chrome & Edge provide (more than 300% zoom), you need to fiddle with it.

Increasing the maximum zoom

In the about:config page, you can increase the maximum zoom level from 300% with two values:

  • zoom.maxPercent, and set to 400 (for 400% zoom)
  • toolkit.zoomManager.zoomValues, is what values the interface uses (the – / + buttons) and add the value 4 at the end for 400%. I use:

That means you can get to 400% (or more) in the browser, which will help to test the new Reflow criteria from WCAG 2.1.

Screenshot of my homepage at 400%
Going to 400% in Firefox

Increasing the default zoom

There does not seem to be an obvious method or configuration for this, the closest I could find is layout.css.devPixelsPerPx.

You have to be very careful with this one, setting something very small could make your Firefox profile unusable.

NB: I wanted this because I wanted to increase the size of mobile twitter in a Firefox sidebar, which doesn’t have it’s own zoom, or inherit from the size you view it in twitter.

I went to bugzilla to post a bug about needing to set default zoom level, and found this 12 year old bug. However, this comment from SeriogaM has a better approach:

Just in case if someone else is tired of hitting Ctrl++ on every new website – here is a simple workaround:

  1. Open Browser Console (Ctrl+Shift+J / Cmd+Shift+J).
  2. On the command line:

To Set Global Zoom (put whatever you want instead of 1.33) enter:


To Reset (back to 1) enter:


A stupidly technical way of setting a default zoom level, I hope the bug gets sorted soon. In Chrome none of this is necessary, you can set the default zoom level and get upto 400% zoom.

3 contributions to “Firefox zoom preferences

  1. > You have to be very careful with this one, setting something very small could make your Firefox profile unusable.

    This happened to me on at least two occasions. I set it to a very large value by accident, and as a result, the entire Firefox UI became so large, it was no longer on the screen. I somehow managed to reset the flag by using the keyboard “blind” (not seeing what I was doing). I hope, there’s a way to reset the flag via the command line, or by editing a file on the disk.

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