Large popups show scroll buttons although they shouldn't

[fmeyertoens]

Sanity checks (must complete)

• [x] I have read and followed the installation instructions in the README
• [x] I have not modified the userChrome.css file
• [x] I have tested the latest release for my Firefox version, or commit on master/beta branch (beta is for Firefox Beta only)

Describe the bug Large vertical popups show scroll buttons at the top and bottom by default in Firefox. MaterialFox tries to hide these: https://github.com/muckSponge/MaterialFox/blob/3eb3971275ae33cd783373cb23473e81d1a6bf88/chrome/popup/popup.css#L177-L180 The .menupopup-scrollbutton selector doesn't seem to apply anymore. In fact I couldn't find an element with this class at all but the selector is used in various other places like global.css and tabbar.css. As the two buttons don't have a class anymore, I suggest using their ID selectors #scrollbutton-up, #scrollbutton-down (or the part selector).

To Reproduce Steps to reproduce the behavior:

1. Make a folder with many entries in the bookmarks toolbar.
2. A scrollbar and two scrollbuttons appear.

System info

• OS: Windows 10
• Firefox version: 76

[fmeyertoens]

Apparently #scrollbutton-up and #scrollbutton-down also apply to the tabbar scrollbuttons, so this is not ideal.

[muckSponge]

Yeah this kinda sucks. Part selector is not supported in userChrome.css. I've used a CSS variable inheritance workaround which assumes all scrollbuttons can have a default visibility set to visible and the parent element (in this case, menupopup) overrides this with a CSS variable. It's not very readable or maintainable but it should work.