Web browser shouldn't be doing it tho.
By the way: You might want to try recording something while walking around with your phone in your pocket. My guess is that your clothing will muffle sound. Any movement will cause fabric to rub against the phone, drowning out the sound you actually want to record. Even if your tactic did work, I'm not sure it would have captured much of the conversation.
Many android phones detect being in pocket and lock screen automatically to prevent accidental touches.
Exactly.
An app which requests the appropriate permissions and gets them granted is really welcome to display this behavior, but not a web browser.
Through the Android permissions system, I can block Firefox accessing my camera or microphone. I do sometimes want Firefox to have access to those things, so I temporarily allow the permissions.