"FirefoxPortable.exe launcher version 2.7.7.0 has a single-instance bug. When Firefox is already open and an external program (e.g. QuiteRSS) tries to open a new link, it shows the error: 'Firefox is already running, but is not responding.' Version 2.6.0.0 works correctly with Firefox 149. Please fix the single-instance handling in 2.7.7.0."
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I just tested Firefox Portable 149 with opening up a file/url while it was already running and it worked without issue. Are you using multiple instances with the manual INI setting? If so, opening files/urls isn't compatible with that mode. It can't reliably be tracked whether a given profile is in use or not and it gets borked easily. This support was dropped a long time ago.
Sometimes, the impossible can become possible, if you're awesome!
Thank you for the quick and accurate response! The issue was indeed the AllowMultipleInstances=true setting in FirefoxPortable.ini. Setting it to false solved the problem completely. I was confused because an older launcher version (2.6.0.0) still worked with that setting, while 2.7.7.0 did not. Now everything works perfectly with the latest launcher. Thanks again!
By the way, in which launcher version was support for AllowMultipleInstances dropped?
Also, would it be possible to re-implement the AllowMultipleInstances support in the newer launcher versions? I understand it may be complex to track whether a profile is in use or not, but it was a very useful feature. Even a limited implementation (without the url/file opening compatibility) would be appreciated. Thank you for considering it!
AllowMultipleInstances support is still included. But I had to lock out the ability to do associations in conjunction with it. I can't reliably determine which profile is in use since Firefox keeps changing what lock files are present within it. And they vary with different extensions. So, you can pick either AllowMultipleInstances or opening URLs/files when it's already running, but not both. You're welcome to look at the code to enhance it.
Sometimes, the impossible can become possible, if you're awesome!
Thank you for the detailed explanation! Now I fully understand the technical limitation — Firefox keeps changing its lock files, making it impossible to reliably detect which profile is in use when AllowMultipleInstances is enabled.
In my case I need both features simultaneously: opening URLs from an external RSS reader (QuiteRSS) AND occasionally running two Firefox