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I'm running Kate under Gnome. Somehow it was resized to a too-large size for my desktop. So now the Maximize and Resize buttons are unreachable. I'm assuming reinstalling would fix the problem, but if I can fix it without reinstalling that would be ideal. Any ideas/suggestions are much appreciated. (I have tried the keyboard shortcuts, with no results.)
If you're using Compiz (used with Unity 3D), there is a nifty plugin that does exactly that, and also moves windows to different parts of the monitor, if desired.
I only know how to set it from CCSM (CompizConfig Settings Manager). You can install CCSM and the compiz plugins by running
sudo apt-get install compizconfig-settings-manager compiz-plugins
The CCSM plugin is called "Put", and is in the "Window Management" section of CCSM.
Enable the "Put" plugin by checking it. Next click the "Put" plugin. You can set a shortcut key in the "bindings" tab for "Put to Next Output". By default, it's disabled, but is easy to set. In this example we've set "Put to Next Output" to Super+Right and "Put to Previous Output" to Super+Left.
If you are not familiar with CCSM, you can get it from the standard repository, but be warned... it can be dangerous to play around with certain settings that you don't understand, so be careful. I've used it a lot over many versions, and can't live without it, but it allows you to chop off your foot if you're not paying attention. don't be too afraid, but don't think it will protect you from yourself.
More info on Compiz: http://wiki.compiz.org/
I found this answer while doing some research into your problem and I thought that it might be of use as while it wont reset the default permissions it will allow you to choose the size of the window when the program is opened.
Best Answer
When a window is bigger than the resolution of the monitor do the following:
Press and HOLD ALT (On Ubuntu 18.04+ Hold SUPER) and then simply click and HOLD the mouse button over the window you want.
Start dragging it until you can see the top part or at least a corner to resize it. Keep holding the corresponding key while doing each click until you can see a corner or the top. From there just resize it as you like.