No, changes you make in the devtools aren't saved and are lost once you reload or leave the page. You can save changes made to CSS files if you use the style editor.

• https://developer.mozilla.org/Tools/Style_Editor

Well style editor seems pretty useless to me! It would be really cool if the inspector section could be save and have a restore to default button and a undo button! please ask your boss if possible for next version.

See Firefox Developer Tools ideas: Top (427 ideas) – Ideas for Firefox Developer Tools:

• https://ffdevtools.uservoice.com/forums/246087-firefox-developer-tools-ideas