In 1.8.4 the ability to increase/decrease font size via keyboard + mouse shortcuts (Ctrl + MouseWheel) was added.
I find this extremely useful as the old eyes often play tricks on me.
I found in my current installation 1.8.5 though, whilst Ctrl+Minus decreases the font size Ctrl+ Plus does nothing.
I downloaded the latest Beta 1.9.0 and I find exactly the same situation.
I tried to see if the shortcuts can be edited somewhere, but I suspect they are hard coded.
Rexlee
This is a known issue:
Until it's fixed you can use ctrl+mouse wheel.
You could revert the change that broke it in the IDE source code and then build the IDE from source if you like.
If you know the solution to the problem I'm sure a pull request with the fix would be much appreciated by all.
With my installation, ctrl-wheel only reduces font size. Moving the wheel either way reduces the font. I can not increase it with ctrl+wheel. When I accidentally reduce the font size with ctrl+wheel, I have to fix it in preferences. This is rather annoying. If the ctrl+wheel were disabled, the problem would be moot. Requested on github.