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

1)Check Firefox sound settings: Open Firefox, click on the three lines in the upper right-hand corner to open the Firefox menu, then click on "Options." Scroll down to "General," and ensure that the "Play sound in web pages" checkbox is selected. 2)Clear your browser cache: Clearing your browser's cache can help to resolve various browser issues, including sound problems. Click on the three lines in the upper right-hand corner of Firefox to open the Firefox menu, then click on "Library," and select "History." Click on "Clear Recent History" and select the options you want to clear. 3)Disable browser extensions: Browser extensions can sometimes interfere with the sound playback on Firefox. To test if this is the case, try disabling your browser extensions one by one and see if the issue is resolved. 4)Update Firefox: Ensure that your Firefox browser is up to date. Go to the Firefox menu, click on "Help," and select "About Firefox." The browser will automatically check for updates and install them if available.