So let understand you can't maximize the screen? If that is the case they you dragged the browser window to large for the maximize feature to work. firefox when install sets a default browser windows size did you change that when it installed? Also did you check that your monitor resolution is set correctly as well. I have firefox and have no issue going from min to max browser size option.

Nish said

there is some gap in between my browser and my window , full screen mode is not available. The gap exist only in the left side and the right side of the monitor. Seems like some browser error . this is also leading to app crash.

True Fullscreen mode using F11 or are you referring to a Maximized window?

Can you attach a screenshot?

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem
• use a compressed image type like PNG or JPG to save the screenshot

Try to rename/remove xulstore.json and if present delete localstore.rdf in the Firefox profile folder with Firefox closed.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:preferences page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox