Tor Launcher monitors and collects log messages from tor. If an ERR or WARN message is generated, a "Copy Tor Log To Clipboard" button is made available on the Network Settings dialog. However, it would be nice to have a built-in log viewer.
One approach would be to log tor messages to Firefox's Browser Console. That would give us filtering and other nice features without any additional development effort. Unfortunately, so far mcs and I have not found a way to open the console when the Tor Network Settings wizard is open (during initial startup). More research is required.
In light of the recent "relay early" attack, some users will really want a way to monitor the tor log in real time. We just committed a stopgap change that additionally routes all of the tor messages received by Tor Launcher to Firefox's Browser Console (I will attach a screenshot to show what the output looks like).
Is it easily possible to add a category?
I see "error", "warning" and "log" for the JavaScript entries, maybe Tor could get its own category.
I don't think so. Looking at the Firefox code, it looks like the set of available categories is fixed. This is a little disappointing. We could switch to the newer console.info(), console.warn() and console.error() API to get the messages broken out by type, but I do not see a way to add a completely new category.
For the record, reason we did not use console.info() and the related function is because they cause the output to include extraneous double quotes which is confusing. See https://bugzilla.mozilla.org/show_bug.cgi?id=977586
One case where this would be helpful: In #22730 (moved), a smart user had a warning about a bogus torrc option, but apparently didn't see it, and therefore thought that Tor hadn't given them a warning at all.