How hot can electronics get?
Virtually all manufacturers data sheets will list both the minimum and maximum storage and operating temperatures for their parts. Further many parts will be available in multiple versions designed to operate in more strenuous environments.

So for example an integrated circuit (IC)may be available in the following versions:

Commercial 0-70°C.
Industrial -40 to +85°C
Military -55 to +125°C.

Needless to say, the cost goes up with increased performance. There are even chips speced for use in outer space. So for example a chip which costs $2 in the "Commercial" grade might cost $2,000 for the version rated for outer space! (As you can guess, they don't sell very many of that grade.)

As to your mouse, generally they try to use the cheapest components possible, so for your mouse 70°C might be the upper limit (it might even be quite less!) which is about 158°F.

One needs to keep in mind that the temperature of the components is affected by two sources:

1) The temperature of the environment.
2) Self heating - some components generate a large amount of heat in operation, CPUs in PCs are one example. This is why they are fitted with big heat sinks and cooling fans to keep them from getting too hot.

As a general rule of thumb, the more power a chip consumes the more heat it generates and the hotter it will get. Of course a mouse uses hardly any power so this should not be a big deal for a mouse.