So I found a workaround with micro-b (others have probably used this already).

1. Type about:config to the taskbar and hit enter. Click the warning understood.

2. Type: browser.enable to the search bar. You will get two options. If the first one for automatic resizing of image is false, click it to activate and hit enter to change the value to true. Close the window.

If you prefer seeing straight the smaller images, you can get now to see too big images fitting your screen like this:

3. Go to a post with too big image. Press the image, chooce "copy image address", click and open another micro-b window and copy (ctrl+v) the address to the taskbar and hit enter.

Or if you do not need to see smaller images straight, you can go to maemo forums Control Panel - Edit Options - untack "Show images" and save. Now you will get only a link to the image and when you click it you get to see it in full and rendered/scaled to fit in open window. I don't know why I didn't do this in the first place. Threads open much faster not loading images.

Now you can view the whole image with micro-b. If the change of the value in about:config doesn't change anything try to first restarting micro-b and if that doesn't make change try rebooting device. I did them both so not sure if they are or aren't needed.