Private Messages, cannot switch from Inbox to Sent?

I'm having problems switching between Inbox and Sent in my private messages since that web page was redesigned. The last time I signed in there were user-friendly tabs for switching between the Inbox and Sent messages, but now there's new drop down menu that is difficult to find and doesn't work correctly.

Whenever I open the new drop down menu and try to hover my mouse over the Inbox or Sent items the drop down just closes before I can select one of those options. Moving my mouse over the menu items (i.e., with one finger on my touchpad) never works, but I finally figured out I could scroll down with a two-finger scroll and keep the menu open so I could tap to select the Inbox or Sent menu items.

This closing drop box problem occurs in my default Firefox ESR v68.9.0 browser (fully patched, Adblock Plus v3.8.4 disabled), MS Edge (the old version, not the new Chromium Edge) as well as IE11.

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64-bit Win 10 Pro v1909 build 18363.836 * Firefox ESR v68.9.0 * Windows Defender v4.18.2005.5 * Malwarebytes Free v3.8.3
Dell Inspiron 5584, Intel i5-8265U@1.60/1.80 GHz, 8 GB RAM, Toshiba KBG40ZNS256G SSD, Intel UHD Graphics 620