I tried it in the current Nightly build on Linux and can confirm that opening a message gives some connecting messages flashing on the tab, but for me it stops after a few seconds and doesn't crash.

Most of the last request seem to be to the "db3msgr5011103.gateway.messenger.live.com" host if I check the Network log in the web console.

Did you try to clear the cache and cookies from websites that cause problems?

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Clearing the cache and cookies did not work. Disabling hardware acceleration did not work. Restarting it in safemode worked. So it's either adblock plus, java, or flash that's causing this then? (those are my only add-ons and extentions).

This would only be true if it works in normal mode with all extensions (Firefox/Tools > Add-ons > Extensions) disabled.
In that case try to find which extension is causing it by enabling one extension at a time until the problem reappears.

Close and restart Firefox after each change via "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: Firefox > Quit Firefox; Linux: Firefox/File > Quit)

In Firefox Safe mode these changes are effective:

• all extensions are disabled
• default theme is used (no persona)
• userChrome.css and userContent.css are ignored
• default toolbar layout is used (localstore-safe.rdf)
• Javascript JIT compilers are disabled (javascript.options.*jit)
• hardware acceleration is disabled

• plugins are not affected
• preferences are not affected

I disabled the extensions and it still crashed. I only have the default theme installed. Hardware aceleration was turned off. So what's left is the .css files and java?

Your plugins like Flash and Java still run in Safe Mode, and .css files are unlikely to make any difference.

Perhaps the problem is with the JavaScript compilers? These are constantly being updated, so a new problem certainly is possible. To selectively disable those:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the search box above the list, type or paste java and pause while the list is filtered

(3) Double-click the following preferences to switch them from true to false:

• javascript.options.baselinejit.content
• javascript.options.ion.content

Note: this is based on Firefox 26. I don't follow developments in Nightly.

Thanks for that jscher2000! Those two options set to false prevent the browser from crashing. So the new JavaScript seems to disagree a little with Nightly, no big deal I suppose? What sort of "adverse effects" would I likely see with these set to false now?

Hi mrobaer, these compilers speed up JavaScript heavy sites, so you'll experience slower response on those sites. You might give it a week and then try reenabling them in case this is a transient problem that will be addressed quickly. I don't know how optimistic to be.