You could try this....
Open your browser window Reduce the size by clicking on the middle button top right. Drag the reduced page to the left hand side of your screen Right click on the top of the reduced page in the space to the right of the tabs etc. Click on size You will then see 5hat your pointer has changed to a "drag" icon Drag the right-hand corner to the bottom right of the screen so that it is full size. Close the browser and re-open to see if it has solved the problem.
By the way when you are still on the same thread you don't have to start a new post - you can just use "reply" at the bottom of the latest post.