It sounds almost like a magnifying glass feature. If this happens on all sites, I would first recommend Firefox Safe Mode to make sure that it is not a result of two addons interacting strangely. *[[Troubleshoot Firefox issues using Safe Mode]] If it does not happen in Safe Mode, it is one of your addons and you can disable and reenable them one by one to find out which one it is. Lastly, can you take a screenshot of what you are seeing, this will help determine what we are dealing with :-) Please see [[How do I create a screenshot of my problem?]] Once you've done this, attach the saved screenshot file to your forum post by clicking the '''Browse...''' button below the ''Post your reply'' box. This will help us to visualize the problem. Thank you!