I've been using Thunderbird for decades, I've donated in the past, and am likely to donate again. With that out of the way, the lack of transparency as to what happens to my money kills the incentive to donate.
"How will my gift be used?"
"Thunderbird is the leading open source email and productivity app that is free for business and personal use. Your gift helps ensure it stays that way, and supports ongoing development."
Well that tells me exactly nothing. This might not be as big an issue if they were separate from Mozilla. To be concrete, and focusing only on the development of Firefox, there's now an AI chatbot in the sidebar. I think that's a good addition. However, when the only options are proprietary services, it's hard for me to see the point of Firefox. It would be easier to get out my credit card for Thunderbird if I didn't have those thoughts in the back of my mind. As it stands, my donation might be going to fund the Mozilla CEO's salary.
> Your gift helps ensure it stays that way
Written this way, it sounds like "donate or we'll have to make you pay for it"
I find that a weird sentiment. Why do people demand to know and control how every one of their donations goes, while nobody questions how corporations use their money. Ironically, the demand for this increased transparency significantly increases compliance cost, which means more and more money is driven away from the actual cause toward the administrative costs. Exactly what people don't want to support.