Hello DavidBE,

I don't remember having to hover over the sub-menus in order for
them to open (but maybe I just never paid any attention to it ....)

It doesn't take any more time or effort to click on them, so I wonder
what the problem is for you (?)

It's the same in Edge's main menu (at least for me).

The problem is that in every other program the sub-menus open on mouse-over of the sub-menu name-and-arrow in the menu, no click, and even in the other Firefox and Thunderbird menus (e.g. the menu bar menus, the tab menus, the context menus in a web page or email) the submenus open on mouse-over, no click, so the behaviour of the hamburger menus in these two programs is different to EVERY other program and even every other menu within themselves. This is plain weird, inconsistent, and means that every time I go to the Firefox or Thunderbird hamburger menu (not a daily need) there's a moment when I mouseover the sub-menu that I want, automatically wait for the sub-menu to open, and only then remember that the hamburger menus in these two programs are the only places i have to click, not just mouseover to open the submenu. It is ... irritating.

Why on Earth do these two programs - and only in their hamburger menus, not the other menus - not behave the same way as all the others, and even not behave the same way as the rest of their own menus? This inconsistency makes NO sense. . And I don't know about Classic Edge as I never used it, but in chromium Edge - Canary and Dev - in the ... menu submenus open on mouseover like everywhere else.

I'm sorry David, please don't get mad at me, but I really can't see how
this is a problem ......

Not that it will make any difference, but I don't use (have nor want) a mouse (I'm a "less is more" kinda girl).

When I have my cursor on the sub-menu; instead of hover, I just click.

I have a trackpad, not a mouse.

There is a standard UI which people expect, unless there's a specific good reason for leaving the standard. One expects minimize/maximize/close buttons in the top right corner of the window, not the top left (in Windows anyway - I've not used Macs or Linux); one expects to get a context menu with right-click, not middle-click; and one expects sub-menus to open on mouseover of the sub-menu name-with-arrow, not to have to click. Like with every other program. LIKE IN EVERY OTHER MENU IN THESE TWO PROGRAMS.

Why is it different for just these programs' hamburger menus? What possible reason is there to break with the standard UI just there and about just that? And if there is no good reason, then they should follow the UI standard like they do in every other way. It is beyond irritating.

David, I hope that someone else will give you the answer/explanation
you're waiting for, cause I don't know what else to say.

Sorry .....

The "3-bar" Firefox menu button drop-down list is a panel and not a normal menu and this means that you need to click to open a sub panel to replace the current content. All panels behave this way like you see if you click the shield icon or the "Site Identity Button" (padlock icon).

You can use the menu bar if you want a normal menu.