How to make permanent changes to a website's CSS from within the browser?

Question

If I am trying to edit some CSS in a huge project using the built-in developer tools in Firefox (which is accessed by right click and then selecting Inspect Element), is there a way to make those changes permanent?

Actually there is a big number of style sheets and and I could not locate this one property in them? I just could not find the file which contains this property, so I want to make permanent changes to the CSS from within the browser. Is there a way?

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EDIT:-

Answer 1

To set up in Chrome first you have to add your project file to a "Workspace", Go into dev tools Ctrl+Shift+I then click on the settings gear and on the left yoou should see Workspace.

After you have added your Project folder into a workspace close out of options and click on the "Sources" tab (still in dev tools)

Now load up your index.html from your LocalHost like you normally would. In the sources panel you should see the currently loaded page and its resources. Right click on your .css file and click "Map To File System Resource" it will bring up a search box where you can search for the corresponding .css file from your actual project folder (that is now part of a workspace in Chrome). Once you make the link Chrome is smart enough to link up any other CSS and HTML files that are in your Project Folder.

Now you can make changes in the Elements tab in Chrome Dev Tools and they changes will persist. Also in the ELements tab it will show you what css file and what line any given Style is originating from!

The best thing about this is if you use Sass or Less then it will map your Scss files back to the CSS styles being processed in Chrome. (please note if using Sass and Less you have to have CSS source maps turned on)