I find info about tricks for Firefox with Leste:
https://leste.maemo.org/Tricks
I might change that user agent hint to something else than Android 9.
But before that I might have many questions: what Firefox version?, from where?, how?

Official from Devuan repos I guess

ah..I needed to write firefox-esr
It is this easy get version 102 (right now)
So in terminal:
sudo apt-get install firefox-esr
And you get it..remember it doesn't made for Maemo UI, so you can think is as backup brownser, if any another browser doesn't open page.

Btw..it shows to net like this:
Mozilla/5.0 (X11; Linux armv7l; rv:102.0) Gecko/20100101 Firefox/102.0
So everybody can think should there change word mobile somewhere, to get more lightweight page from server.

I tested Firefox 115.4ESR with Pinephone Keyboard.

Works fine, not have Maemo UI, but you can get full-screen with F11 key, to get it F11 work you need fix keyboard layout:
https://talk.maemo.org/showpost.php?...1&postcount=46

I did not make any tricks what found in Leste wiki. By default you can scrolling with keys. With touch screen you only select link (or select text for copy) with touch screen. And actually that is very handy for copy-paste (with ctrl-C and ctrl-v) that way.

Firefox 115 might work also with Droid4. It is too much for N900, still hoping that somebody try make old Maemo Firefox Fennec version to Leste.

Firefox ESR 115.9 has strange screen update issue that is not with version 115.8. Sometimes newer version needs go to full screen (I use Pinephone Keyboard F11) and back before new link is opened. Also going to full screen is little bit slower.

Firefox ESR 115.9.1 seems fix that screen update issue. There is still one issue. You can not pull down pull-down menus, but they work this way: touch pull-down menu and use arrow keys to change what is selected.

I tested also that version with Droid4. Works fine, but screen feels quite small without full screen. Full screen works, but how to get back windowed mode? Current keyboard layout missing F11, but that might no be only problem, because I connected external keyboard and I press F11 and it close Firefox.

I found out that F6 is official full screen button in Maemo (that is what Nokia 770, N800 and N810 Full-screen key send) so if somebody what make Maemo customization to Firefox, it would be good idea.