Found this for the bookmarks menu size, hope it helps.

https://www.userchrome.org/firefox-89-styling-proton-ui.html

Reducing vertical spacing in menus

Most of the menus in Firefox 89 are shorter, but you still may prefer smaller gaps between the items, especially with long lists like Bookmarks. The main reason items are more widely spaced is the padding along the top and bottom of each item. There is a temporary preference in Firefox 89 to roll back the changes to some menus, and for more control or in future versions of Firefox, you can use custom style rules in a userChrome.css file.

Here are the steps to switch the temporary preference between the older menu appearance and the Firefox 89 ("Proton") appearance:

   In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.
   In the search box in the page, type or paste browser.proton.contextmenus.enabled and pause while the list is filtered.
   Double-click the preference to switch the value between true (Proton style) and false (Photon style).

This reverts the menus to their previous spacing and color scheme:

thank you for your reply...."accept what Risk"..??

The alteration that is being proposed is unsupported and could fail to work in the future.

Then why would anyone offer this as a solution....And why does firefox use this format as its technical support for user issues. Volunteers....you guys dont get paid to do this...Did you even know that firefox was going to dump a new version on everyone.?? Did they even tell you of any user options with this new version..?? Hey...firefox...if you are reading this....Fix the issues....also....shame on you....truly lousy user support.

Hi

I would not recommend that fix, but the option is there if you want it.

We did know about this update for some time, I have been using for quite a while now and really like it.

I cannot speak for all of the team, but I like contributing to the Mozilla project and helping make the web better for everyone.