I recommend the Zoom Page addon ( https://addons.mozilla.org/en-US/firefox/addon/zoom-page/ ). You can zoom with ctrl+mouse wheel and your prefered zoom level will be remembered for each web site.

In case you use "Clear history when Firefox closes" or otherwise clear history.

• do not clear the Site Preferences

• Options/Preferences -> Privacy -> Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an "Allow" exception you may want to keep