Image rendered differently in firefox than in chrome

First, please tell me if this belongs in another community, but since the problem happens in a browser I felt more appropriate to post here than in graphic design.

I bought a theme to make a quick website, but wanted the provided background-image to be a bit lighter. Armed with gimp and limited knowledge, I fiddled with the brightness/contrast and came to a satisfying result. I saved the file with a simple ctrl-S (didn't change the filetype or anything).

In chrome the result is as expected. In firefox, somehow the contrast seems way up and the image looks much more purple?

Here is a screenshot of the problem, left is in gimp, middle is in firefox, right is in chrome.

Here is the file, not in a screenshot:

I am very curious as to why this is happening, and how to fix it it, because the result in firefox in far inferior than in chrome!

Thanks in advance to anybody who can help!