Firefox 57 (Quantum) is missing a font from it’s newtab page and from fonts from other pages fail to display; here’s a quick fix. Update: turns out to be a sandboxing issue (see end).

Firefox 57 Quantum

Font Problem

If you’ve just installed Firefox 57 like me (on Kubuntu 17.04) you may be a little disoriented – it’s different.

font display error in Firefox 57

For me it was a little too different the about:newtab page, set as my start page (see image), lacks a font it’s instructed to use. Here’s how to work around that.

Which font is missing?

So, I’d just updated to Firefox 57 and assumed that maybe it wasn’t finding one of my fonts for some reason. Using the developer tools we can see the font SegoeUI is missing:

SegoeUI font is missing leaving a sparse page

Where’s he go? (“segoe”)

In case you missed it that’s an hilarious pun … but anyway … SegoeUI it turns out is a Microsoft Windows font given away with the likes of Word, Excel, Windows 7 and 8 (but not 10 according to Microsoft, see link). I checked in my “about:config” on Firefox and it turned up with no hits, so it’s not my config. Perhaps Mozilla have chosed SegoeUI font as some sort of hidden default.

How to fix it?

Look in your font preferences

Ya don’t say! Well, yes I do:

uncheck to prevent pages over-ruling your font preferences as a quick fix

Alt > Edit > Preferences : Language & Appearance > Advanced … (or use the “burger” menu to open “preferences” then go from there) will open the above dialog box. If you uncheck the option “Allow pages to choose their own fonts, instead of your selections above” and force your choice of fonts then you’ll at least be able to see the text on pages.

Your other option would be to install SegoUI, eg you might search for SegoeUI.ttf and download and install the font file, but you need copyright permission to do that. Most Microsoft Windows users will have the file.

There should be a third option of fixing Firefox so it doesn’t try and use a non-installed Font … I’ll post details if/when a fix or workaround of that nature presents itself.

Woo-hoo fixed fonts

That should do it. If you chose the install option then you should be able to go back to your fonts preferences (above) and re-check the box to allow websites to select the font they use. Your Firefox should now show all the fonts, it just might not show the correct ones for a while.

Postscript – perhaps it was me

Defective font file?

SegoeUI font showing on the newtab page in Quantum

When I came to install the segoeui.ttf font (which I have from a previous Windows purchase) I noticed that I actually had that file. Attempting to open it with kfontview failed, it appears the font file was corrupted somehow (worrying, must check my SMART status for my disks). After reinstalling my newtab page and other pages are showing properly, well showing in the new Firefox 57 way:

Update: Sandboxing

Turns out that I wasn’t the only one with the problem and there were several bug reports about it. The most pertinent is probably this one: “Firefox 57 sandbox causes issues with fonts from TeXLive” on bugzilla.

For me the fix was, once I’d done the above, to clean up the directories which my fonts were in, somehow over time they’d become mixed up and weren’t in a place that Firefox was allowing itself to look, in other words the sandbox settings were preventing the font files from being properly accessed (and a bug was preventing Firefox from realising that and moving on down the font-family to use the fonts that could be accessed).

I didn’t have to do anything else, but looking at the bug there are several other options for fixing the issue if it presents in different ways for you. Most commonly either altering the sandbox level or adding the font directories to the sandbox whitelist.

Hope you got it fixed!

Please comment if this helped, especially if you can add a tip for other users.