re :Latest upgrade version 83.0 I somehow think you have provided the 'Mozilla Firefox' browser latest update information.

You have posted the comment in the 'Thunderbird' email client Support forum. The latest Thunderbird release is 78.5.1

Are you having a problem with Firefox browser or Thunderbird email client ?

re :has increased vertical space between lines on a screen If you are talking about Thunderbird email client then you need to be more precise. Are you talking about one specific area in Thunderbird eg: Thread Pane ? If yes, then I have already informed you how to fix it. But just in case you have forgotten: Lengthy conversation at the following link with information on how to fix. https://support.mozilla.org/en-US/questions/1307570

You did post a question about this about a month ago and you stopped corresponding and did not provide information when requested. https://support.mozilla.org/en-US/questions/1311441

re :Should I submit a bug report? No. It is highly unlikely this has anything to do with a bug. You need to be accurate with information. You need to correspond in this forum in this question. That means providing information when requested.

You need to explain whether you used the information at the link provided to create a 'userChrome.css' file containing the necessary code. I still have no idea what you did or did not do. saying "The problems have remained. Please help!" does not tell me anything about whether you have followed instructions.

Did you create a chrome folder as instructed in your 'profile name' folder? If yes, post image showing it's location.

Did you create a 'userChrome.css' file containing specific code as advised and saved it in that 'chrome' folder? If yes, then post image showing it's location in the chrome folder and make sure the 'View' is set to show 'Details' and the column header called 'Type' is visible. Then post an image showing the contents of the 'userChrome.css' file.