You can use custom style rules to modify the toolbar area, and apply those to Firefox using either the Stylish extension OR a userChrome.css file. Stylish is convenient for development due to its handy preview feature, but if you prefer to completely avoid any additional extensions, userChrome.css is a built-in option.

You might want to create two rules, one which hides the bars normally and another which displays them when you hover a certain area. Unless someone has written the rules already, I suspect some trial and error will be involved.

Some resources to get you started:

• http://kb.mozillazine.org/UserChrome.css
• https://github.com/JasonBarnabe/stylish/wiki

By the way, you can find helpers on the following forum (categories in the left column): https://forum.userstyles.org/

Thank you for your reply.