Here are a few things you can try to fix the issue:

1)Clear Firefox cache: Clearing your cache can help to free up space on your computer, improve your browsing speed and fix the problem you're experiencing. Go to the Firefox menu, click on "Options," then "Privacy & Security," and under "Cookies and Site Data," click "Clear Data." Make sure to check the boxes next to "Cookies and Site Data" and "Cached Web Content," then click "Clear." 2)Disable Firefox extensions: Sometimes, a faulty Firefox extension can cause the browser to behave erratically. To test if an extension is causing the issue, disable them one by one and then check if the problem is resolved. Go to the Firefox menu, click on "Add-ons," then "Extensions," and disable each extension one by one. 3)Disable hardware acceleration: Firefox uses hardware acceleration to speed up the performance of the browser, but it can cause issues like the one you're experiencing. To disable hardware acceleration, go to the Firefox menu, click on "Options," then "General," and uncheck "Use recommended performance settings." Then uncheck the "Use hardware acceleration when available" option. 4)Reset Firefox: Resetting Firefox to its default settings can help to fix the issue you're experiencing. Go to the Firefox menu, click on "Help," then "Troubleshooting Information." Then click "Refresh Firefox" at the top of the page. 5)Reinstall Firefox: If the above solutions do not work, you may need to reinstall Firefox. To do this, first, uninstall Firefox from your computer. Then, download the latest version of Firefox from the official website and install it on your computer.