• Empty Cache
• Reset security.sandbox.content.level back to default
• Reset all settings for Fonts back to Default
• Close and restart Firefox then close again, do below.

uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 57.0.2 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

Special icons are usually supplied by a special icon font that is downloaded from the server (@font-face) You may see little boxes with the hex code of the character if you do not have a font installed that covers this Unicode range.

You can check gfx.downloadable_fonts.enabled on the about:config page and make sure it is set to true (if necessary double-click the line to toggle its value to true).

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

If locally installed fonts aren't working then this is possibly a sandbox security issue.

You can set this pref to 2 or 1 on the about:config page to lower the sandbox security setting.

• security.sandbox.content.level = 1
• close and restart Firefox to make the change effective.

If '1' still doesn't have effect then try '0' to disable the sandbox.

If this didn't work then undo/reverse the change and reset the pref via the right-click context menu to the default value.

Hey guys,

thanks for the replies.

I've checked about:config and "gfx.downloadable_fonts.enabled" is true, the other point I already tried with no luck.

@Pkshadow: Thanks for your reply as well, but I just got the same display error again, so your suggestions didn't help completely. :-( Do you have any more ideas? Could it be possible that my Firefox profile is the cause of the malfunction?

Thanks again!

You can check the Web Console (Tools -> Web Developer) for messages about blocked content and about the presence of mixed or unsafe content.

• "3-bar" menu button or Tools -> Web Developer
• https://developer.mozilla.org/en/Tools/Web_Console

You can check the Network Monitor to see if CSS and Font content is blocked or otherwise fails to load.

• https://developer.mozilla.org/en/Tools/Network_Monitor

If necessary use "Ctrl+F5" or "Ctrl+Shift+R" to reload the page and bypass the cache to generate a fresh log.

ECfnW said

The only thing that actually helped is changing the default font of all websites in the settings, but this isn't a valid option either since all websites looks stupid after that change.

Are you using the setting to override the fonts on web pages with your own preferred fonts? Otherwise, you probably would not see a big effect of changing your default font.

Or maybe the problem is blocked by a setting or extension. Consider:

(1) Built-in Tracking Protection feature. See a shield icon toward the left end of the toolbar when this problem hits? More info: What happened to Tracking Protection?.

(2) Content blocking extension such as Blur, Disconnect, Ghostery, NoScript, Privacy Badger, or uMatrix. You can view, disable, and often configure or remove extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. Then cast a critical eye over the list on the right side. Any extensions that Firefox installs on its own are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything that could be blocking fonts? If in doubt, disable.

Any improvement?

What font is this about?

You can right-click and select "Inspect Element" to open the builtin Inspector with this element selected.

You can check the font used for selected text in the Font tab in the right pane of the Inspector. Note that this is not about the CSS rule that specifies the font-family, but about the font that Firefox tries to use as shown under the Font tab.

• https://developer.mozilla.org/en/Tools/Page_Inspector/How_to/View_fonts

Thanks a lot for your answers. I just started Firefox for the first time today & I opened 4 different tabs and one tab was messed up.

cor-el said

You can check the Network Monitor to see if CSS and Font content is blocked or otherwise fails to load.

I can't confirm this, since the CSS file was loaded correctly according to the monitor.

jscher2000 said

Are you using the setting to override the fonts on web pages with your own preferred fonts? Otherwise, you probably would not see a big effect of changing your default font.

No, this checkbox is checked, so websites can use their own font.

jscher2000 said

(1) Built-in Tracking Protection feature. See a shield icon toward the left end of the toolbar when this problem hits? More info: What happened to Tracking Protection?.

This icon isn't in the toolbar in the tab which is messed up, so no.

jscher2000 said

(2) Content blocking extension such as Blur, Disconnect, Ghostery, NoScript, Privacy Badger, or uMatrix. You can view, disable, and often configure or remove extensions on the Add-ons page. Either:

As far as this is considered only four addons should have to do with this: AdBlock Plus, Ghostery, WOT & YesScript2. But I disabled them all, re-loaded the tab (Ctrl+F5) & nothing changed. When I open the website in a new tab, all is fine - I can't recreate the messing up when I want to.

cor-el said

What font is this about?

On this particular it's about Tahoma, so not a very special font at all.

Thank you very much!

ECfnW said

As far as this is considered only four addons should have to do with this: AdBlock Plus, Ghostery, WOT & YesScript2. But I disabled them all, re-loaded the tab (Ctrl+F5) & nothing changed. When I open the website in a new tab, all is fine - I can't recreate the messing up when I want to.

Oh, that is hard to explain. The next time, if you reload the page bypassing the cache -- Ctrl+Shift+5 -- does that also resolve the issue?

jscher2000 said

Oh, that is hard to explain. The next time, if you reload the page bypassing the cache -- Ctrl+Shift+5 -- does that also resolve the issue?

Do I get you right? I should bypass the cache if a website is all messed up - right?

If so, that's what I already tried several times, with no luck. Everything is loaded like normal (CSS files etc.) but the website is still messed up and no fonts are visible. :-(

Did you try if you can possibly select the text in case there is a problem with the text color being transparent?

Can you attach a screenshot with the Inspector window showing a part with the missing text and the Fonts tab?

cor-el said

Did you try if you can possibly select the text in case there is a problem with the text color being transparent?

Yes, I already tried this. It kinda looks like it, because I can see that the text is selected but still no text visible.

cor-el said

Can you attach a screenshot with the Inspector window showing a part with the missing text and the Fonts tab?

Please find the attached image from a German website I visited a couple of minutes ago where it happend again. The arrow in the screenshot from left to right is the marked row in the inspector, the other arrow is the headline of the next column.

I really hope this can help you a bit more?

Thank you very much! :-)

So, I assume that you can copy the selected text to the clipboard and paste it elsewhere?

Do you have this Verdana font?

You can do a font test to see if you can identify corrupted font(s). This website uses the Shockwave Flash plugin.

• http://browserspy.dk/fonts-flash.php?detail=1

You can try different default fonts and temporarily disable website fonts to test the selected default font.

• Options/Preferences -> General: Fonts & Colors -> Advanced
  [ ] "Allow pages to choose their own fonts, instead of my selections above"

cor-el said

So, I assume that you can copy the selected text to the clipboard and paste it elsewhere?

I guess so, but I can't remember if I already tried this. I will do this as soon as another problem occurs and I'll edit it in here.

cor-el said

You can do a font test to see if you can identify corrupted font(s). This website uses the Shockwave Flash plugin.

• http://browserspy.dk/fonts-flash.php?detail=1

Yes, I have the Verdana font. Since I installed Windows 10 on my computer I never touched the installed fonts anyway.

According to the website, 178 fonts are installed. Please find the attached screenshot of the complete result.

Thank you very much!

ECfnW said

cor-el said

So, I assume that you can copy the selected text to the clipboard and paste it elsewhere?

I guess so, but I can't remember if I already tried this.

I will do this as soon as another problem occurs and I'll edit it in here.

Since I can't edit my old post, here we go. ;-) I just restarted Firefox and of course one of the websites ran into this error.

And you were right, I can copy the text into Notepad, Word, whatever - that works fine. If I disable the checkbox "Allow pages to choose their own fonts, instead of my selections above" the font, which is set within preferences, shows up and all the text is back on the website, without refreshing whatsoever.

Did you try the font test to see if something unusual is going on?

Does it have effect in such a case when you temporarily disable downloadable fonts in case something is interfering?

• gfx.downloadable_fonts.enabled = false

Note that this affects websites that use special icon fonts.

You can check for sandbox security related issues.

You can set this pref to 2 or 1 on the about:config page to lower the sandbox security setting.

• security.sandbox.content.level = 1
• close and restart Firefox to make the change effective.

If '1' still doesn't have effect then try '0' to disable the sandbox.

If this didn't work then undo/reverse the change and reset the pref via the right-click context menu to the default value.

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

I tried both settings and it worked, but the second or forth tab went blank again. So nothing really helped.

It's getting really annoying. :-(

I would normally expect to see under result a sample of what the fonts look like if show details is selected, but I only see a font list in your screenshot.

• http://browserspy.dk/fonts-flash.php?detail=1

I would still suspect that there is an issue with some fonts. If deselecting the website fonts works then this is either a problem with the locally installed font that is specified or downloaded via @font-face or something else goes very wrong.

Are only a few fonts used in cases when this happens if you check the Fonts tab in the Inspector or is this randomly (i.e. sometimes a specific fonts works and sometimes nothing is shown)?

You can try to disable hardware acceleration in Firefox.

• Options/Preferences -> General: Performance
  remove checkmark: [ ] "Use recommended performance settings"
  remove checkmark: [ ] "Use hardware acceleration when available"
• https://support.mozilla.org/en-US/kb/performance-settings

Close and restart Firefox after modifying the setting to make the change effective.

• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can check if there is an update for your graphics display driver and check for hardware acceleration related issues.

• https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

Firefox 52+ has changed from Cairo to Skia for canvas/content rendering.

• https://www.mozilla.org/en-US/firefox/52.0/releasenotes/
• When not using Direct2D on Windows, Skia is used for content rendering

You can modify these gfx.*.azure.backends prefs on the about:config page to revert to the old font rendering swap the skia,cairo order to cairo,skia or remove the skia and leave cairo.

• gfx.canvas.azure.backends = direct2d1.1,cairo,skia
• gfx.content.azure.backends = direct2d1.1,cairo,skia

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

cor-el said

You can try to disable hardware acceleration in Firefox.

• Options/Preferences -> General: Performance
  remove checkmark: [ ] "Use recommended performance settings"
  remove checkmark: [ ] "Use hardware acceleration when available"
• https://support.mozilla.org/en-US/kb/performance-settings

I already read your comment yesterday evening and of course I applied those changes immediately. Since I changed this option like you wrote, I haven't had the problem since and I opened 100+ tabs in the last 12 hours or so.

If this would be the solution, that'd be great and a great way to end 2017. :-D

Thank you very, very much for your help cor-el. Like I said in my last post, two days later I haven't had a corrupt tab, that's why it seems to be fixed and I've already chosen your answer as solution.

Thank you very much again and a happy new year. ;-)