The default behavior for links/URLs in tickets should be that they open in a new window or tab. Ideally this behavior could be switched on or off at a user level, but in any case it'd be better to have it on by default than off by default.

This subject has already been brought up multiple times in other forum posts but each time it gets shot down for bad reasons, most notably:

• We tried it and were met with resistance - Changes to existing/expected behaviors are always met with some resistance. Complaints aren't a sign that something is bad for all users, they're a sign that some users are annoyed, and it's almost always because of a deviation from the expected. Let a change rest for a couple of months and see if they keep complaining, pay attention to whether new users even notice or care, remember that happy users don't take the time to write you to express their pleasure, and ensure you're catering to the majority of users and use cases instead of just the noisier users.
• We engineered a work-around that avoids one problem that not opening in new windows causes - Great, but that one problem isn't the only problem, plus there are other benefits to making the change. Incidentally, that feature also makes it impossible to author two or more tickets simultaneously, which is something I commonly want to do as one thing reminds me of another, or one issue is similar to another, etc.
• Imposing this behavior is a usability no-no - This is silly... it's fortune-cookie usability that fails to account for actual user goals and behaviors, and favors the 5% of users and use cases over the 95% (or whatever the real numbers are, but I imagine this isn't far off). It's true that opening links into a new window by default reduces the options available to a user since there's no "open link in same window" context-menu option. But fewer options does not equal bad usability. If you're assessing usability/UX, you have to look at how and why people are using something. What are users doing when they're interacting with tickets that have links in them? Why are there links in tickets? What would a user's goal be in clicking one? Links in tickets are there for reference related to the content of the ticket—to connect people to resources, examples, screenshots, etc. They are interacted with in the context of interacting with a ticket. How often, if ever, is a person's intent in clicking on a link in a ticket to stop their interaction with the ticket and move onto something new? By opening a link in the same window, you remove the user from the context of interacting with that ticket, and force them to either jump back and forth between the ticket and the linked page ("pogosticking") or to have to take additional cognitive and interaction steps to open the link in a new window. Both of those things are "usability no-nos." You're avoiding imposing a low-friction behavior on a small percentage of users and use cases by imposing an annoying behavior (and the requirement to remember to do it each time) on the majority of users and use cases.

Sorry to snark at you but if you're going to shoot down reasonable requests for an obvious and easy-to-implement feature, please don't use UX pseudo-science to do it.