Display formatting symbols (invisible characters) on webpages and text forms
I don't know of any browsers that will show invisibles, but there are work-arounds. Since you are already "using various online tools for translation and proofreading," I assume you are also copy and pasting between the tools. The easiest solution would to just paste the text into a different text editor as an intermediate step. This should reveal tabs vs. spaces, and different types of line endings.

This will not show the difference between non-breaking spaces and spaces, though. You could view the source and search for "&amp;nbsp;" but that will be hit or miss, because people aren't consistent.