It's more than ads. With ublock origin in advanced mode you can easily block images and javascript (except on sites you whitelist). On mobile, that makes a lot of difference; the data usage can easily become half or even less than you'd have with Chrome, and because of that it also loads much faster. It can be the difference between nearly hitting your monthly data cap or ending the month with plenty of data to spare.
Even without Ublock, Firefox Android supports extensions, so I can toggle an image blocker extension during those lean times when I'm close to hitting my monthly data cap.
Unfortunately, I've found that Firefox is a bit slower to render pages than Android Chrome, and scrolling experience sometimes feels janky. That said, it's unlikely that Android Chrome will ever support ad blocking, so Firefox will stay on my device.
I tried to be the good guy on mobile and put up with ads for years. But I recently installed uBlock because I almost couldn't even read the content anymore.
Agreed. Erstwhile ad-free websites like BBC News for example now have an annoying full-page ad on mobile with a requisite tiny "Close" button. The worst part is, the news article loads before the ad, so you can see the article text and image for ~1 second before the screen flashes white and the full-page ad loads. That's a fail on so many levels, it's far simpler to view the site on on Firefox Android with Ublock Origin enabled.
BTW I have the BBC news site whitelisted on desktop because the ads are not nearly as intrusive and UX-breaking.
The breaking point for me was a neverending barrage of autoplaying, unstoppable video while on the subway. Now it's not just intruding on my own patience, it's pretty rude to everyone around me and I can't make it stop.
