Thunderbird 151.0.* doesn't accept "/" for first search of message

I've been using T-bird since nearly the beginning, and I've always been able to search for a string in a message by hitting the slash ("/") and typing my search string. This appears to be a shortcut for Ctrl+F (on Windows, currently Windows 11). With T-bird 151.0, when I press "/" it is ignored... the first time I use it. If I press Ctrl+F and do a search, then I can start all subsequent searches ''in that message'' with a slash. If I close that message and open another, I must again use Ctrl+F the first time I want to search. My muscle memory constantly forces me to type "/<string>" to search, but since T-bird ignores the slash, the following characters immediately take action, usually causing me to navigate away from the message, mark them as read/unread or as junk, etc. Since I can use "/" on subsequent searches, I'm thinking this is a bug, not a feature removal. Can this be checked/confirmed? ...thanks!