Some possible solutions include:

1)Clearing your cache and cookies: Go to the Firefox menu and select "Preferences." Under the "Privacy & Security" tab, click "Clear Data." Make sure to select "Cookies and Site Data" and "Cached Web Content" to clear. 2)Disable extensions: Some extensions can slow down your browsing experience. To disable them, go to the Firefox menu and select "Add-ons." Select the extension you want to disable and click "Remove." 3)Disable hardware acceleration: Go to the Firefox menu and select "Preferences." Under the "General" tab, uncheck "Use hardware acceleration when available." 4)Try to disable DNS over HTTPS (DoH) : Go to the Firefox menu and select "Preferences" then select "Privacy & Security" tab. Search for "DNS over HTTPS" and select "Enable" 5)Check for malware: Use a reputable anti-malware program to scan your computer for malware.