Safely customizing Tor-browser possible?

Hi all! I’m a new to tor-browser user.
I’m wondering about a couple of things namely (this will be fairly long): Is it safe to customize the Tor browser toolbar, example: enabling the menu bar and bookmark bar? I quite like the default TBB layout, I’m just asking is it ok security-wise to add and remove stuff from the toolbar? The Tor browser manual says you can add the noscript icon in the toolbar for easy access, I’ve done that, but what about everything else? It doesn’t say anything about customization using the Firefox customize mode.
In Firefox one can customize userChrome.css. I read on the web you can do that in Tor browser too, but the person said he can’t guarantee the security of the browser when doing so. What are people’s take on this feature, is it safe to use, should it be avoided? Again, not that I’m going do it, the default UI is quite good.

Another thing I’d like to do is to disable smooth scrolling and the full-screen fade in and out when watching videos. In about:config there is the full-screen-api.transition-duration.enter value that you can set to “0 0” and full-screen-api.transition-duration.leave that can also be set to “0 0”. In my opinion those should be 0 by default since not even Chrome has the fade in feature. This feature is just a distraction as is smooth scrolling. If it changes the fingerprint changing those settings however I’m of course not going to change them.

Finally on the Tails website it says changing the security level of Tor browser changes the finger print, is that true or is the Tails browser somehow different? Link: (Why is javascript enabled by default?) Tails - Frequently asked questions
When searching the forum I found this thread talking about bookmarks and customization, only the bookmark concern was replied to, which is why I’m posting a new thread. Link: Saving bookmarks, customize toolbar

That’s all for now, I might have more questions later…