Some Firefox themes can become incompatible when Firefox updates. In some cases, addons can also change the appearance of Firefox. To test if this is what is causing the issue, please try the steps found in this Mozilla support article: *[[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]] Firefox can also be modified using Cascading Style Sheets, which are files that set the styling rules for the different elements of the Firefox browser and all websites. If there is a custom CSS file applied to Firefox, it will be located in the <code>chrome</code> folder in your Firefox profile folder. Please check if this folder exists in your Firefox profile. If it does, rename the <code>userChrome.css</code> file inside the folder (if it exists) to <code>userChrome-backup.css</code>. If this does not fix the issue, rename the file back to <code>userChrome.css</code>. '''NOTE: '''You will need to restart Firefox before the CSS solution will take affect. For more information on locating your Firefox profile, please refer to this Mozilla support article: *[[Profiles - Where Firefox stores your bookmarks, passwords and other user data]]