FullCalendar fcicons font warnings in Firefox console

Ethsim2 · July 15, 2026, 9:53pm

When visiting the Upcoming Events calendar in Firefox, I see repeated warnings concerning the FullCalendar fcicons font.

Tested page:

/upcoming-events/week/2026/7/13

Installed version

Discourse 2026.7.0-latest +314
Git commit cf0d9228b4
Ember v6.10.1

Console warning

downloadable font: Glyph bbox was incorrect; adjusting (font-family: "fcicons")

The warnings reference glyphs 4, 5, 6, 7, and 10.

The calendar appears to continue functioning normally.

This matches an existing confirmed FullCalendar issue:

github.com/fullcalendar/fullcalendar

Warning in Firefox console: Glyph bbox was incorrect

opened 02:16PM - 24 Feb 25 UTC

indigoxela

Confirmed Alt Environment

### Reduced Test Case https://fullcalendar.io/demos ### Do you understand that… if a reduced test case is not provided, we will intentionally delay triaging of your ticket? - [x] I understand ### Which connector are you using (React/Angular/etc)? No connector (vanilla JS) ### Bug Description While doing some early testing with v7.0.0 I realized some browser console nagging in Firefox. ``` downloadable font: Glyph bbox was incorrect (glyph ids 4 5 6 7 10) (font-family: "fcicons" style:normal weight:400 stretch:100 src index:0) source: data:application/x-font-ttf;charset=utf-8;base64,... ``` It has nothing to do with actual functionality (calendar works fine). And actually there's the same nagging with v6.1.15, so nothing newly introduced. I just never realized so far. The nagging can be easily observed in the default demos - with Firefox. I hope, this is the right queue for such a report? Font-family fcicons probably means, this font is custom - or is this based on some really old font-awesome glyphs?

There is also an open pull request containing a proposed fix:

github.com/fullcalendar/fullcalendar

Fix fcicons font to not generate warnings in Firefox (#7955)

main ← cketti:fix-font-warning

opened 01:25AM - 26 Jun 25 UTC

cketti

+1 -1

The `fcicons` font contains glyphs with bounding boxes that are too small for it…s contents. This might be a bug in the tool that created the font (IcoMoon?). Browsers use [OpenType Sanitizer](https://github.com/khaledhosny/ots) to sanitize font data. Firefox is outputting some of the warnings in the developer console (see #7895). I used OpenType Sanitizer ([ee75ff5dcef67fcd3ea7255044c889349e210750](https://github.com/khaledhosny/ots/tree/ee75ff5dcef67fcd3ea7255044c889349e210750)) to fix up the font data in `icons.css`. You should be able to recreate this change using the following commands: ```shell # Extract base64-encoded font data, decode it, and write to fcicons.ttf grep -oP '(?<=base64,)[^"]+(?=")' icons.css | base64 -d > fcicons.ttf # Use OTS to sanitize fcicons.ttf; write result to fcicons-sanitized.ttf ots-sanitize fcicons.ttf fcicons-sanitized.ttf # Update icons.css with the sanitized font data sed -i -E "s#base64,[^\"]+#base64,$(base64 -w0 fcicons-sanitized.ttf)#" icons.css ``` Fixes #7895

The FullCalendar issue was opened on 24 February 2025 and the proposed fix was submitted on 26 June 2025, but both remain open.

I am reporting this separately from a request-rate-limiting issue because the two console messages appear unrelated.

Presumably this will require the upstream fix to be merged and included in a FullCalendar release before Discourse can receive it. Is that correct?

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FullCalendar fcicons font warnings in Firefox console

Installed version

Console warning

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