There are two ways you can bookmark a page in Firefox.
Method 1:
1. Click to Bookmarks in the menu bar, then click on Bookmark This Page…

2. Rename the bookmark to whatever you like and save it in the folder of your choice.

Method 2:
1. Go to the page you would like to bookmark and hold down the Ctrl and D buttons on your keyboard.

2. Rename the bookmark whatever you like then put it in the correct folder.