In the past I have donated on a monthly basis to Mozilla, around 15$.
However, due to obscene CEO pay during a massive decline in Firefox's market share, as well as very questionable privacy and diversification (thus loosing focus on their core product) moves over the years, I stopped donating a few years back.
If Mozilla were to lower CEO compensation, and shift focus more towards the browser, as well as position themselves better when it comes to privacy, then I would consider donating again.
Lastly, Mozilla should have a way for donations to be marked specifically for Firefox, rather than them going into a big pool.