[gcb0]

Yes. As it always been for any software.

Host files: as secure as you can get. Whole network.

Browser extension: remote code exploit possibility. Probably not available for mobile. Trusting someone who takes money from Google...

[fpgeek]

FYI, on mobile, Adblock Plus and Adblock Edge (among others) are available for mobile Firefox.

[gcb0]

For how many browsers?

And then they have even less community validation, rising the security tradeof even more