You need to provide steps and a doc that we can access to see if we can replicate the issue. I can load Google Sheets. see screenshot

Edition Windows 11 Pro Insider Preview Version 22H2 Installed on ‎29-‎Nov-‎22 OS build 25252.1000 Experience Windows Feature Experience Pack 1000.25252.1000.0

1. The issue is not loading the window in your screenshot. It is loading the icons in the Google Sheets toolbar that I included in a screenshot in my original message. I've attached a full screen screenshot.

2. There aren't really any steps to explain. When I open a new or existing Google Sheets document, the icons in the toolbar are not visible.

"icons in the toolbar are not visible" was the info missing from your description.  ;-))

I put sheets in full screen mode and it looks like your issue. Please verify.

No. That is not my issue.

I don't have the toolbar icons hidden. If you look at my screenshot, you will see that about 10% of the icons are visible in their correct position.

Did you try Firefox in Safe Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_how-to-start-firefox-in-4troubleshoot-modesf5safe-modesf

What OS?

1. I just tried safe mode but it made no difference. 2. Mac OS 12.6

Is the issue with one of your docs or does it also happen with a blank sheet example in GS?

Let me pop on my old mac running 10.13.6 and see what happens.

It happens with all Google Sheets - new and old.

It doesn’t happen on my MacBook running Mac OS 13

Such small icons are usually supplies by a special iconic font, so if you do not see those icons then it is likely that you are blocking remote fonts that are downloaded from the server.

Make sure you allow pages to choose their own fonts.

• Settings -> General -> Language and Appearance -> Fonts -> Advanced
  [X] "Allow pages to choose their own fonts, instead of your selections above"

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock Plus, NoScript, DuckDuckGo PE, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

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

• https://firefox-source-docs.mozilla.org/devtools-user/web_console/

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

• https://firefox-source-docs.mozilla.org/devtools-user/network_monitor/

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

Make sure you allow pages to choose their own fonts.

• Settings -> General -> Language and Appearance -> Fonts -> Advanced
  [X] "Allow pages to choose their own fonts, instead of your selections above"