If you happen to like having the menu bar enabled in Firefox, but would prefer to keep the Bookmarks button to the far right of the address text box visible, there's a simple tweak you can apply that'll quickly sort you out.
By default, the Bookmarks button is hidden when the menu bar is turned on. Ghacks posits the reason for this is that you can use the menu bar's "Bookmarks" option instead, though this might do crazy things to your muscle memory. Fortunately, Ghacks shows us that fixing this user interface quirk is very straightforward.
First, you'll need to open your profile folder for Firefox, which can be accessed quickly by typing "about:support" into Firefox's address bar and then, once the support page has opened, selecting the "Show Folder" button.
In the profile folder, you'll need to create a directory called "Chrome" if it doesn't exist. Open the new folder and create a new text document named "userChrome.css" (again, only if it's not there, otherwise, just edit it). Then, it's just a matter of adding a line and restarting the browser:
Open it and add the following line to the end of it.
Once done save it and restart the browser. You should notice that the bookmarks icon will remain visible now in Firefox’s address bar.