Theme Font & Size Changer

Theme Font & Size Changer Project Image

Theme Font & Size Changer is a simple browser tool that lets you change the font size and font family of Firefox. It is especially valuable tool for visually impaired people and wide screen users.

There are three places that you can manage the global font size and font family of Firefox via Theme Font & Size Changer. Add-on Bar icon, toolbar button and Tools menu option. All font size and font family changes are instantly applied and they are saved permanently and through sessions.

Different from add-ons that enlarge and reduce text on web pages, Theme Font & Size Changer changes the font size and font family in all windows, menus, toolbars, etc within Firefox itself.

It was initially created to be an accessibility aid for persons with visual impairments and for those without perfect eyesight, but it’s also useful for Firefox users with high monitor resolution settings and wide screens.

While Theme Font & Size Changer was written to be used with Firefox default theme, it does work with other non-default themes, but you may come across issues where some elements within Firefox retain the (non-default) font size setting that the theme developer chose for their theme.

There are three places that you can manage the global font size and font family of Firefox via Theme Font & Size Changer:

• Add-on Bar Button: Click on the Theme Font & Size Changer button to open up Theme Font & Size Changer settings panel.

NOTE: Add-on Bar resides at the bottom of the Firefox window. Add-on Bar is the old status-bar. If Add-on Bar is not visible, you should activate it. To do so, choose View menu from Firefox Menu Bar and hover over the Toolbars option and click on the Add-on Bar option if there is no tick. If you are Windows 7 user, you should click on the orange Firefox button at the top of the window and hover over the Options and click on the Add-on Bar option if there is no tick.

• Tools Option: Choose Tools menu from Firefox Menu Bar and click on the Theme Font & Size Changer option. It will open up Theme Font & Size Changer settings panel.

• Toolbar Button: It is optional so it is not visible as default. If you want to place a Toolbar Button, right click on a toolbar button like Home Button, then choose Customise option. A window will pop up. Find the Theme Font & Size Changer button, then click and drag the Theme Font & Size Changer button in the toolbar of your choice and drop the button. Clicking on this Theme Font & Size Changer button will open up Theme Font & Size Changer settings panel.

In Theme Font & Size Changer settings panel, Font section provides fonts currently installed on your operating system. With this option set, you will be able to fine tune your font family of Firefox theme.

In Size section, simply select a font size value (from 6 to 80 pixels) and the changes will be applied instantly and globally.

No known compatibility issues with the following themes:

NASA Night Launch
Kempelton Large
Mostly Crystal
Walnut for Firefox
Ambient Fox Xyan
Themes by Aaron Spuler

There are no known compatibility issues with Personas skins.

Special thanks to Ken Saunders for the priceless contribution and testing efforts.

Install Theme Font & Size Changer

31 Responses to “Theme Font & Size Changer”
  1. avijit hazra says:

    This is really nicee…

  2. Pamela Williamson says:

    I love the instant font changer, I have to wear glasses and this help me a great deal not have to get so close to the screen!

  3. Asmae Chob says:

    This add-on is perfect, i really do like it…the best one about themes in firefox, thx baris derin

  4. CT Ward says:

    Theme font changer is awesome! Frank Lyon stopped making his for FFX 3.
    I am legally blind and so appreciate the help!
    I’m a legally blind photoartist. Check it out and read my profile.
    Thank You!

  5. Jawadick says:

    I really like for this stuff

  6. JamPhel says:

    it is really a great addson, i like it. thanks for the designer and the Firefox Group.

  7. George says:


    i noticed that in new version has been added localization infrastructure. I already have translated this tool for my personal use, but how can i submit my translation? I can’t find information about this somewhere..


  8. frankwhite says:

    this is really wondeerful

  9. Inoudo says:

    I was having a hard time with wide screen HD monitor seeing the iddy biddy font.

    It works great for my Thunderbird. Thanks Much!

  10. janvier25 says:

    I love being able to set the fonts and my brain is organized by colour, but I find the black font on the unselected tabs difficult to read. Would it be possible set the unselected tabs to white or yellow?

  11. […] Click Here to Download Theme Font & Size Changer 1.2 […]

  12. SAMEER says:

    Dear Baris,
    Thanks for update….
    Great job.

  13. Michael Kinsman says:

    Thank you for “Theme Font & Size Changer.” My wife is visually impaired, and this is a life-changer for her.

    Apparently it has not been updated for Thunderbird 6.0. Will that change occur in the near future?

    Again, my thanks for your thoughtfulness in providing this add-on.

  14. sinz54 says:

    I would like to support your efforts with a small contribution.

    Unfortunately, your link takes me to a version of PayPal that’s in the Turkish language, which I cannot read.

    Do you have a method of payment that involves a website in English?

  15. steve says:

    Great program, excellent solution.
    You can expand this program and solve another problem that no one else has done: miniscule cursors in Firefox and Thunderbird.
    ON a high pixel density monitor, say 24″ or 30″, the system cursor looks “normal” when set to 64 x 64 pixels.
    however, when your cursor mouses onto a Thunderbird window, the cursor shrinks down to abut 16-18 pixels and is hard to see.
    Search google, and many people ask for solutions to this.

    It would fit in good with your program (more than any other Thunderbird extension) if, in addition to font and size changes, you can set the cursor theme and size.
    Please look into adding this to your fine program!
    Steve Mitchell

  16. Lorene Kraft says:

    I looked for hours before finding this and had almost given up hope. Thank you so much.You have provided a wonderful service. Could I donate by paypal? Thanks again

  17. Martin Tatum says:

    Thank you for “Theme Font & Size Changer” [standing ovation, fireworks & brass band]. For those of us who have imperfect vision this extension is essential. I would be very grateful if this extension could be used in “Thunderbird” and especially “Songbird.” Will it work in these now? May the Lord bless and keep you.

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