Existing tabs are not connectable after an install or extension update

[fregante]

I don't know if this is tracked somewhere, but #5899 extended this bug to every page:

• ensureContentScript fails on *.pixiebrix.com after an extension reload #4189

I think it's not a great experience for a new user to install the extension and see an error on every page.

This happens because Chrome does not automatically inject the content scripts to existing tabs

Fun facts:

• Firefox does automatically run extension in existing tabs
• I created a package for this a long time ago https://github.com/fregante/webext-inject-on-install (it's a little out of date but it likely still works)

Demo:

Screen.Recording.4.mov

[fregante]

I'll address this soon together with #5041, unless you prefer not to.

[grahamlangford]

I think this would be great. Especially with our current focus on the developer persona. Are there any performance concerns with adding this change that we should be aware of?

[fregante]

That made me think we should probably not target every tab at once but rather:

1. track the open and non-discarded tabs
2. manually inject into the active/visible tabs
3. listen to tab focusing to inject PB as needed

This is slightly more involved than forEachTab(injectScripts) but I think it's worth it to avoid long CPU spikes.