It's been a while since i've used the mic feature in the chats. And being on Ubuntu i don't know if there will be any differences. But what i often had to do was right click the mic button and there were options given under there. This is where i wold turn on mic/webcam.
Also, make sure, before you enter the rooms, that you have 'high speed' on, as turning it to low speed turns off all cam abilities. And make sure the other two options are set right. By default they should all be on, but it's always good to double check.
If this doesn't help, then i hope someone more knowledgeable comes along with the right answer.