Site is???

https://www.katsuichi.co.jp/

Did you try Firefox in Troubleshoot Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#search104 Works for me. see screenshot What security software are you running? If Windows Pro version, try testing in Windows Sandbox (VM) to see if you have the same issue. https://www.howtogeek.com/399290/how-to-use-windows-10s-new-sandbox-to-safely-test-apps/

yes! Troubleshoot mode is NoProbrem!

However, when I opened many pages on other sites, it crashed in the same way. and,katsuichi.co.jp is immediately.

Since I just migrated my PC, I don't have any security software installed, only Windows Defender.

yes! Troubleshoot mode is NoProbrem!

Sounds like an add-on is causing the issue. What is your PC? Laptop, Desktop, or DIY? What make and model, if not DIY? If Windows Pro version, try testing in Windows Sandbox (VM) to see if you have the same issue. https://www.howtogeek.com/399290/how-to-use-windows-10s-new-sandbox-to-safely-test-apps/

I tried in troubleshoot mode. and that problem didn't happen

I also tried the same in sandbox. I installed Firefox in a sandbox, logged in and synchronized, and tried it, but no problems occurred either.

windows10pro64bit desktop(dell precision3450)

If you access the Facebook login page or the login screen for editing our homepage, it will crash immediately.

MOZ_CRASH Reason: assertion failed: self.fonts.templates.has_font(&shared_font_key)

The crash appears to be related to fonts.

Reset fonts to default by going to Windows Control Panel > Appearance and Personalization > Fonts > Font Settings > Restore default font settings.

Try changing gfx.e10s.font-list.shared and gfx.font-list-omt.enabled to false in about:config then restart the browser.

I solved the problem by doing as instructed. thank you.

Sore wa yokatta desu ne!  ;-)) Mark it as resolved and have a nice day.

You are fantastic customer support!　thank you!

Nihon to onajiyōni.  ;-))