Thanks a lot for that detailed (researched) feature request! I see you looked into the source… 😉

tipSaveQrCode: put a 'Save' button in popup window

Good idea, but issue is stuck at finding a good and minimal UI. See/follow #225 for details.

tipQrCodeHotkey: move to settings page, and explain how to configure.

For the given space explaining the latter would be too much, but maybe an entry in the FAQ could help? That could also be linked? (ref #67)
For moving well they are shown in both places, actually it could even be configured how much in both contexts, but I did not do so, yet. Likely, because, IMHO, it is also relevant to users, who have never seen/used these options before and just may discover an easier way to use the extension.
Actually IMHO that is the main aim of that tip – not to let users change it, that is something not everyone may care about (though may be a good low priority tip) –, but to let users know of that feature initially.

tipYouLikeAddon, tipTranslateAddon, tipDonate: put as links in either settings page, popup window, or both.

Not done as IMHO it would partially be too intrusive. Only as very little links at the bottom, but IMHO that would also not fit into the style.

Preserving fixed space for the tips can be an option, instead of randomly hiding tips.

I decided against that as the UI should be minimal and wasting space for that not very likely event of such a tip being shown is literally just a waste of screen space. The resizing was less bad IMHO.

Generally

In general, please be aware the likelihood to see such a prompt like the "rate me prompt" is very low and e.g. only shown after you have used the extension for sometime and not shown again if you have dismissed it once.
They are really kept to a minimum and many users do e.g. not know that they can help the add-on and support it by writing a review.

That is why I did not found it necessary to have a feature in there to disable that. So either the rules to show that need to be fine-tuned or I would also not be generally be opposed against such a settings, just remember every option comes at a cost. But probably that old more a test-thing monospace options could be removed – I mean I naturally have no data for it, but I doubt anybody actually uses it… 🙃