I use microsoft edge almost exclusively. Firefox is my back-up, almost always during poor weather conditions including the hours building-up to fairly heavy rain. This is because edge is finicky about security protocols and seems unable to read all of them when connecting to a site (any website) during poor weather conditions. It will return a message about the site's certificate apparently out of date. Firefox, though, will be able to connect to the same site. On the occasions that it can't, I assume there's some technical hitch at the website, and try again a few hours later. And things are okay.
That said, I have experienced the missing quote button on occasion. I restart my laptop, not shut down and start. That works for me.
My more frequent problem is when I try to copy a whole post by manually highlighting end to end : the moment I highlight the first letter of the post, all the details of the person who made the post including their image automatically gets highlighted. I work around that by highlighing from the second letter onwards, then filling in the missing letter after pasting (in a word file) or inserting the quote into a new post for the thread.
It's curious how the same browser works differently for folk.