I will sign it in a minute and I see a lot of people don't care about it as they don't want to monetize their website or they use ad blocker anyway but this is how I see it because it can affect everyone in some way.
Scenario 1:
The website you love visiting each day might be relying on ads. Due to this change firefox are making, they may not have enough revenue to keep the website going and might be forced to shut it down due to it.
Scenario 2:
There are loads of free hosting sites, some awesome ones like IcyBoards which are able to offer free forum hosting because of the revenue they make from advertisements. With this change, they may not be able to afford to keep the service going and may either shut down or start charging. The customers are affected because they might not be able to afford it, thus having using the free host in the first place or if the host shut down, they can't use the service. If it was a free host, there is a chance they had no access to the files and couldn't back up the site.
This can also go back to scenario 1.
I can't change your decision but hopefully my point will help.