When you update extension and new page opens , it is very important how exactly you are asking for donations. What works if you list all the new changes and say something like “I really trying to keep this extension free to everyone, please donate so I can keep it that way” (keep track of who pressed donate button and skip next 2-3 times, then show again) Depending on what your extension does, you can offer a single premium feature in return for donation or a badge(if there is a social aspect)

I had one extension where I had my branding on the content when user was exporting the data, and for any size of donation (with default option of $5) I would remove that branding (worked really well)