profiler VS devtools

Probably your best bet is to use the Firefox Profiler once it starts hogging the CPU to try to see what it's doing. I'd be happy to take a look at the result although I don't have a lot of experience at diagnosing performance problems; hopefully the profile will make it obvious what's going on.

I tried using the https://profiler.firefox.com/ and running with:

You can try to reproduce while taking a profile using the Firefox profiler, then share it in the #perf:mozilla.org room on Mozilla's Matrix instance.

Run a profiling session for ~30 sec when you notice something is running slower than you expect, see https://profiler.firefox.com/. Share results here if you want help interpreting them.

Next time, send a SIGABRT to the main process (kill -6 $(pidof firefox)) and use the resulting backtrace (you will find a link to the crash report in about:crashes) to file a bug. A performance profile could be useful, but you'll need to know first what to capture. This seems like a graphics issue, so try the Graphics preset. Share a link to your report.

https://profiler.firefox.com will be useful if you can capture and share it to developers.

If you can reproduce it in safe mode and a clean profile, capture a performance profile using the clean profile while trying to load a problematic webpage, don't remove any information from it, and share it here (although it's typically not easy for users to analyse them), or file a bug with it attached.

Next time, capture a performance profile using the Graphics preset, and kill the browser by entering kill -6 $(pidof firefox) in a shell. This will create a bug report (unless debian disables the crash reporter) that would indicate where Firefox is stuck at. You might need to use an official build to get useful results.

Not at this time. I'm pretty full up at this point with day job ( https://replay.io ), conferences, and personal life stuff.

My current ongoing Redux maintenance task is trying to revamp our "Redux Essentials" tutorial to be TS-first. Making slower progress on that than I'd wanted, but hopefully can get that wrapped up in the not _too_ distant future.

Beyond that, we've got a ton of open RTK Query feature requests that I'd like to address later on this year.

Exactly - that's what we've already built for web development at https://replay.io :)

I did a "Learn with Jason" show discussion that covered the concepts of Replay, how to use it, and how it works:

- https://www.learnwithjason.dev/travel-through-time-to-debug-...

Not only is the debugger itself time-traveling, but those time-travel capabilities are exposed by our backend API:

- https://static.replay.io/protocol/

Our entire debugging frontend is built on that API. We've also started to build new advanced features that leverage that API in unique ways, like our React and Redux DevTools integration and "Jump to Code" feature:

- https://blog.replay.io/how-we-rebuilt-react-devtools-with-re...

- https://blog.isquaredsoftware.com/2023/10/presentations-reac...

- https://github.com/Replayio/Protocol-Examples

Replay's founders originally worked as engineers on the Firefox DevTools (and in fact our debugger client UI started as a fork of the FF Devtools codebase, although at this point we've rewritten basically every single feature over the last year and a half). So, the original Replay implementation started as a feature built into Firefox, and thus the current Replay recording browser you'd download has been our fork of Firefox with all the recording capabilities built in.

But, Chromium is the dominant browser today. It's what consumers use, it's devs use for daily development, and it's what testing tools like Cypress and Playwright default to running your tests in. So, we're in the process of getting our Chromium fork up to parity with Firefox.

Currently, our Chromium for Linux fork is fully stable in terms of actual recording capability, and we use it extensively for recording E2E tests for ourselves and for customers. (in fact, if you want to, all the E2E recordings for our own PRs are public - you could pop open any of the recordings from this PR I merged yesterday [0] and debug how the tests ran in CI.)

But, our Chromium fork does not yet have the UI in place to let a user manually log in and hit "Record" themselves, the way the Firefox fork does. It actually automatically records each tab you open, saves the recordings locally, and then you use our CLI tool to upload them to your account. We're actually working on this "Record" button _right now_ and hope to have that available in the next few weeks.

Meanwhile, our Chrome for Mac and Windows forks are in early alpha, and the runtime team is focusing on stability and performance.

Our goal is to get the manual recording capabilities in place ASAP so we can switch over and make Chromium the default browser you'd download to make recordings as an individual developer. It's already the default for configuring E2E test setups to record replays, since the interactive UI piece isn't necessary there.

Also, many of the new time-travel-powered features that we're building rely on capabilities exposed by our Chromium fork, which the Firefox fork doesn't have. That includes the improved React DevTools support I've built over the last year, which relies on our time-travel backend API to extract React component tree data, and then does post-processing to enable nifty things like sourcemapping original component names even if you recorded a production app. I did a talk just a couple weeks ago at React Advanced about how I built that feature [1]. Meanwhile, my teammate Brian Vaughn, who was formerly on the React core team and built most of the current React DevTools browser extension UI, has just rebuilt our React DevTools UI components and started to integrate time-travel capabilities. He just got a working example of highlighting which props/hooks/state changed for a selected component, and we've got some other neat features like jumping between each time a component rendered coming soon. All that relies on data extracted from Chromium-based recordings.

[0] https://github.com/replayio/devtools/pull/9885#issuecomment-...

[1] https://blog.isquaredsoftware.com/2023/10/presentations-reac...

I made a Replay recording of the sandbox:

Hiya folks! In addition to all my free time spent working on Redux, answering questions, and modding this sub, my day job is working on Replay.io. Today we're thrilled to announce our new Replay for Test Suites feature, which lets you record and time-travel debug Cypress (and Playwright) E2E tests as they ran in CI!

FWIW, the Firefox devs who were doing the WebReplay time travel debugging POC weren't, as far as I know, fired. Instead, they left and started Replay ( https://replay.io ), a true time-traveling debugger for JavaScript.

I joined Replay as a senior front-end dev a year ago. It's real, it works, we're building it, and it's genuinely life-changing as a developer :)

Not sure how well this would have fit into Firefox as a specific feature, given both the browser C++ runtime customizations and cloud wizardry needed to make this work. But kinda like Rust, it's a thing that spun out of Mozilla and has taken on a life of its own.

Obligatory sales pitch while I'm writing this:

The basic idea of Replay: Use our special browser to make a recording of your app, load the recording in our debugger, and you can pause at any point in the recording. In fact, you can add print statements to any line of code, and it will show you what it would have printed _every time that line of code ran_!

From there, you can jump to any of those print statement hits, and do typical step debugging and inspection of variables. So, it's the best of both worlds - you can use print statements and step debugging, together, at any point in time in the recording.

See https://replay.io/record-bugs for the getting started steps to use Replay, or drop by our Discord at https://replay.io/discord and ask questions.

I also recently did a Learn with Jason show episode based on this, where we went through many of the same topics, and also looked at the Replay.io time-traveling debugger that I build as my day job:

My day job is working at a company called Replay ( https://replay.io ), and we're building a true "time traveling debugger" for JS. Our app is meant to help simplify debugging scenarios by making it easy to record, reproduce and investigate your code.

I currently work for Replay.io, where we're building a true time-travel debugger for JS apps. If you haven't seen it, check it out - it makes debugging so much easier, and I've solved many bugs that would have been impossible otherwise