Same thought train like people claiming a protest march does nothing. You couldn't be more wrong. Making your opinion heard and showcasing how many people are with you has impact.
In fact, I'll turn your logic upside down: if your protest didn't get the result you wanted, you just didn't mobilize enough people (or not enough people cared for your cause)
Bollocks. For example in Germany, online petitions on a government run website that reach a certain threshold of people signing are automatically discussed in parliament.
And in the Firefox case here, no idea what they are planning but they could for example hand over the printed out signatures or dump them in the politicians post box or whatever. Have some fantasy.
In Russia change org was one of very few channels to bring change into politics.
For some reason our politicians actually listened to those. So it was a very useful tool.
Unfortunately, I don't have much idea how effective it is since Feb of 2022. Imagine our gov as an armodillo. It has a sturdy shell, so it is very hard to get good changes through it's head. Now that armodillo closed up in a ball, it lives in it's own bubble, its being fed by it's own lies. Nothing good can come out of that head. And it doesn't.
Petitions have weight providing they're coming from the right places. There's a difference between the random internet petitions that random users make, and petitions coming from bodies such as unions or regulatory bodies.
This is a petition being put forward from a well known organisation, so I would gather it actually has some weight.