If Firefox is your main Internet browser and you use Picture in Picture mode quite often. This article will show you how to quickly and easily change the font size of captions in Picture in Picture mode. By default PIP mode captions in Firefox are huge which makes watching and reading content quite difficult.

Related: How to make the Firefox tab bar smaller. Change the Firefox Proton tab bar size.

Picture in Picture mode in Firefox is quite a handy addition to the browser as it allows you to watch content in a smaller window while you browse other content on websites. However, if you are trying to use Picture in Picture mode in Firefox with closed captions, you’re going to need to change the default font size. By default, Firefox is using a rather large font which is essentially all-consuming on smaller screens when PIP is being utilized.

Thankfully it is possible to change the font size that Firefox uses by default when Picture in Picture mode is active, which allows you to scale things down to a more usable size for your particular device. On smaller screens, this is especially handy. The steps below will show you how to change subtitle size in Picture in Picture mode in Firefox for Windows, Linux and macOS. They are the exact same for every device, which is a nice touch.

Note: You will have to wait until Firefox version 101 is released to make the change. Which should be the 31st of May 2022 if things don’t change.

How do you change the font size of subtitles in Picture in Picture mode on Firefox? (Windows, macOS, Linux)

In order to change the font size of subtitles (captions) in Firefox PIP mode, you’ll need to do the following.

  • First, open Firefox, then type about:config into the address bar and press Enter.
  • Next, accept the risk warning (nothing to worry about). It’s just a disclaimer in case you change something and ruin your browsing experience. Worst case scenario, you just reinstall Firefox.
  • Now copy and paste the text below into the search box and press Enter.


  • This will bring the option to the top of the page and allow you to change the settings. Simply type Small to change the font size to small or Largeto make it even bigger. By default, it is set to Medium.

can you change subtitle caption size in picture in picture mode firefox

  • Finally, click the tick to save the change, Restart Firefox and you’ll have smaller or bigger captions/subtitles the next time you’re using Picture in Picture mode in Firefox.

If you access this location and notice that you don’t have the option to change from Small, Medium or Large, you are using the wrong version of Firefox and will need to wait until the feature is rolled out to the stable release. If at any stage you wish to revert back to the default settings, just go back to the exact same location and set it back to Medium.

How do you create desktop shortcuts for different Firefox profiles?

If you happen to have more than one Firefox Profile and want an easy way to switch between them. Make sure you check out the following article which will guide you through the process quickly and easily.
How to create a desktop shortcut for specific Firefox profiles.