I must honestly say that paying monthly for features that don't require monthly payment is kind of cheap, like i would rather pay 10$ for lifetime of using my own pictures rather than paying monthly for something that I can achieve by modifying the plugin or just not using it. The plugin has no features that should require monthly/renewable payments like updating a Dictionary or a service like cloud settings-sync (it does have the last mentioned feature, but it could easily be achieved by using the Firefox Account Sync for example, or being able to export a settings file). Because of this, I am kind of disappointed, because I don't want to pay monthly just to be able to pick my own images and my own font, and as such I feel it isn't worth it paying for this as none of the other features available are what I want/need, and since you cannot just buy the features you want and are forced for a monthly payment, I will rate this addon low, as this simply is a bad excuse to earn more money on features that are static that do not cause any expenses to the developer because of our (the User's) usage. But, I guess since the addon is working fine beyond that, I can at least give it 2 stars.

EDIT: Also, I noticed afterwards that the behavior is a little different from the Chrome version, for example it hijacks your Home-Page which is inherently annoying and thus doesn't make it worth having this addon installed at the time of writing this, at least not just for a little nicer "New-Tab" page.

I guess for now I will have to disable Momentum until that Home-Page issue is fixed, because that is by far the most annoying thing, it greatly surpasses the stupid paywall.