I would like to take this. Can you please guide me, as it is my first time i am contributing.
Should i replace it from every place listed in the link you have provided above?

Thank You,
Kartik Gautam

(In reply to Kartik Gautam from comment #1)

I would like to take this. Can you please guide me, as it is my first time i am contributing.

Hi Kartik! You can check out https://firefox-source-docs.mozilla.org/contributing/contribution_quickref.html for an overview of all you need to make your first patch. Please let me or Emilio know if you have more specific questions.

Should i replace it from every place listed in the link you have provided above?

Everything that's not in the "Test files" category in the link should be replaced.

Can You please help me, i am confused what should be commit message.
Is below message okay ?
hg commit -m "Bug 1677247 Replace :not(:is(X)) with :not(X) in the codebase. r?xyzabc"
And whom should i add as reviewer ?

Thank You,
Kartik Gautam

(In reply to Kartik Gautam from comment #3)

Can You please help me, i am confused what should be commit message.
Is below message okay ?
hg commit -m "Bug 1677247 Replace :not(:is(X)) with :not(X) in the codebase. r?xyzabc"
And whom should i add as reviewer ?

Looks fine, emilio should be a good reviewer for this patch.
Also, most people usually add the dash between the bug number and the first word.

So: hg commit -m "Bug 1677247 - Replace :not(:is(X)) with :not(X) in the codebase. r?emilio"